Osmosis and Its Applications

Osmosis and Its Applications, Fig. 1 Forward osmosis profiles of the solution concentration and the osmotic pressure under the effects of membrane stmetures and orientations, (a) A symmetric dense semipermeable membrane with only ECP effects, i.e., concentrative ECP and dilutive ECP. (b) An asymmetric membrane with the dense-selective layer (DSL) facing against draw solution (normal mode) with the profile of the solution concentration illustrating concentrative ICP and dilutive ECP. (c) An asymmetric membrane with the porous support layer (PSL) facing against draw solution (reverse mode) with the profile of the solution concentration illustrating dilutive ICP and concentrative ECP. The key parameters Ch... 

Osmosis and Its Applications, Fig. 2 Schematic illustrations of 2-D simulation domains of reverse osmosis, forward osmosis, and pressure-retarded osmosis. The... 

Osmosis and Its Applications, Fig. 4 Schematic of power generation principle for a forward osmosis power plant [9]... 

This chapter is concluded therefore with the following statement. Although membranes with electric charges are well established in reverse osmosis and nanofiltration applications, the fundamental aspects of membrane formation and membrane transport are still in its infant stage. 

The emergence of reverse osmosis is a major scientific event in the field of applied chemistry and chemical engineering all applications and technology of reverse osmosis arise from the science of reverse osmosis a fundamental approach to the science of reverse osmosis, and the development of this science in all its aspects based on such approach are absolutely necessary for the effective utilization of reverse osmosis for any application whatsoever. To present this point of view is the object of this lecture. 

Filtration can remove fine suspended solids and microorganisms, and microfiltration membranes of cellulose acetate or polyamides are available that have pores 0.1-20 /xm in diameter. Clogging of such fine filters is an ever-present problem, and it is usual to pass the water through a coarser conventional filter first. Ultrafiltration with membranes having pores smaller than 0.1 fim requires application of pressures of a few bars to keep the membrane surface free of deposits, water flows parallel to the membrane surfaces, with only a small fraction passing through the membrane. The membranes typically consist of bundles of hollow cellulose acetate or polyamide fibers set in a plastic matrix. Ultrafiltration bears some resemblance to reverse osmosis technology, described in Section 14.4, with the major difference that reverse osmosis can remove dissolved matter, whereas ultrafiltration cannot. 

Electrophoresis has the greatest practical applicability of these electrokinetic phenomena and has been studied extensively in its various forms, whereas electro-osmosis and streaming potential have been studied to a moderate extent and sedimentation potential rarely, owing to experimental difficulties. 

In some applications of reverse osmosis and ultrafiltration spiral-wound modules in the food industry, it may be desirable to allow a small portion of the feed solution to bypass the module to prevent bacteria growing in the otherwise stagnant fluid. One way of achieve this bypass is by perforating the ATD as illustrated in Figure 3.45 [115]. 

Figure 3.42 Exploded view and cross-section drawings of a spiral-wound module. Feed solution passes across the membrane surface. A portion passes through the membrane and enters the membrane envelope where it spirals inward to the central perforated collection pipe. One solution enters the module (the feed) and two solutions leave (the residue and the permeate). Spiral-wound modules are the most common module design for reverse osmosis and ultrafiltration as well as for high-pressure gas separation applications in the natural gas industry...

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