Membrane techniques, application

Ashraf Chaudry, M., Ahmad, S., Malik, M. T. (1997). Supported liquid membrane technique applicability for removal of chromium from tannery wastes. IfOste Management 17 211-218... 

The use of reverse osmosis (RO), electrodialysis reversal (EDR) and other membrane techniques, and evaporation or demineralization may be applicable when a reduction in the TDS content of the MU water source is required. 

The preparation of food for consumption, as well as manufacturing of various products from different raw materials, usually involves the application of several discrete unit operations and processes. Many operations, such as washing, trimming, milling, leaching, disintegrating, mechanical separation, and use of membrane techniques, may decrease the natural toxicity of some raw materials by eliminating specific undesirable components. Examples include the removal of most of the fluorine compounds from Antarctic krill... 

Membrane Processes [109,110]. Depending on the desired application, membrane techniques can be divided into ... 

Belafi-Bako, K., Nemestothy, N., and Gubicza, L. 2004. A study on applications of membrane techniques in bioconversion of fumaric acid to L-malic acid. Desalination 162, 301-306. 

Raghava Rao et al. [89] selectively removed neutral salts contained in spent chromium tanning solutions to achieve a more efficient technique for recycling the unused chromium and process water. The electrodialysis unit contained Neosepta CL-25T and ACH-45T membranes. An application of 13-30 V to a 5 dm solution over a period of 5 - 6 h produced currents between 2 and 4 A 90% of the sodium chloride and 50% of the sodium sulfate were selectively removed with minimal transport of Cr(III) species across the membranes. Addition of EDTA to the spent liquor as well as periodic reversal of electrode polarities eliminated membrane fouling. 

Membranes prepared by the majority of the established methods have limitations in their pore sizes. To make membranes with finer pore diameters suitable for more demanding separation and membrane reactor applications, a widely practiced technique is to modify the pores or the surface of an existing membrane structure which has already been made. This encompasses a variety of techniques. Some of them are based on gas or vapor phase reactions. Others modifications occur in liquid phase. Some progress having pore diameters in the molecular sieving range has been made. 

The micellar-enhanced ultrafiltration MEUF technique, based on addition of surfactants and chelating agents to complex and enhance removal of undesirable compounds, show considerable promise in membrane degumming applications. The natural substances such as phospholipids act as surfactants to form large micelles that will be rejected by the membrane. 

Separation processes are widely used in industry. Chanical conversions often run incompletely as dictated by the thermodynamic equilibrium or by the wish to obtain high selectivity, which may require relatively low corrveraon or the application of one of the reactants in excess Separation methods include distillation, crystallization, centrifiigation, extraction, adsorption and membrane techniques. 

An overview of selected membrane techniques for environmental applications Measured fluxes are independent of severe fouhng and virtually independent of concentration up to 100 g/L total solids... 

Carbon dioxide separation from the air, mixtures with CH4, N2, O2, has been studied from both biological and engineering applications. Spiral-type FLM, HFLM, and capillary membrane techniques were tested for these purposes. 

To make an appropriate choice of the membrane technique (or determine its applicability to water or wastewater treatment), it is essential to be aware of the physicochemical and biochemical properties of the solute and its components. Having such information at hand, we may consider the technical parameters of the available membrane processes. 

It seems worthwhile to give detailed characteristics of the available membrane techniques and, also, to analyze their current and potential applications to environmental engineering in general or, specifieally, to low- and no-waste technologies directly related to environmental engineering. 

On analyzing the validity of the data included in the figure, it is obvious that we can argue about the position of UF. What raises serious objections is not so much the magnitude of sale, as the predicted drop of the dynamics of sale. UF belongs to those membrane techniques which offer great possibilities, and there is hope of extending their applications to new areas, e.g. to separation in wastewater treatment processes. Th e exist a number of industries —... 

There are a number of different membrane techniques which have been suggested as alternatives to the SPE and LLE techniques. It is necessary to distinguish between porous and nonporous membranes, as they have different characteristics and fields of application. In porous membrane techniques, the liquids on each side of the membrane are physically connected through the pores. These membranes are used in Donnan dialysis to separate low-molecular-mass analytes from high-molecular-mass matrix components, leading to an efficient cleanup, but no discrimination between different small molecules. No enrichment of the small molecules is possible instead, the mass transfer process is a simple concentration difference over the membrane. Nonporous membranes are used for extraction techniques. 

The author discusses application of ELM, SLM, and polymer inclusion membrane techniques in separation of metal ions (precious metals, Cu, Ni, Zn, Pb, Cd, Cr(VI), Pu, Am, etc.) and organic pollutants (phenols and its derivatives, carboxylic acids, antibiotics, etc.) from wastewaters using laboratory, pilot, and industrial scale modules. Effects of experimental variables upon the solute flux for the various types of liquid membranes are analyzed. The author discusses potential and commercial aspects of hquid membrane technology in wastewater treatment. 

Valenzuela, F., Basualto, C., Tapia, C., Sapag, J. (1999). Application of hoUow-fiber supported liquid membranes technique to the selective recovery of a low content of copper from a Chilean mine water (Short communication). Journal of Membrane Science 155 163-168. 

Blatt, W.F. et al. "Solute Polarization and Cake Formation in Membran Ultrafiltration Causes Consequences and Control Techniques," Ultrafiltration Membranes and Applications, Polymer Science and Technology, Volume 13. 

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