Reverse osmosis advantages

Some desalination plants combine distillation with reverse osmosis to produce both power and water. Multistage flash (MSF) processes are used to produce both power and distilled water. The combination of RO and MSF and the advantages of such a combination have been reported (111). 

Given the first type of simulation, it is advantageous to be able to design a system of RO modules that can achieve the process objective at a minimal cost. A model has been iategrated iato a process simulation program to predict the stream matrix for a reverse osmosis process (132). In the area of waste minimization, the proper placement of RO modules is essential for achieving minimum waste at a minimum cost. Excellent details on how to create an optimal network of RO modules is available (96). 

Electrodialysis. In reverse osmosis pressure achieves the mass transfer. In electro dialysis (qv), dc is appHed to a series of alternating cationic and anionic membranes. Anions pass through the anion-permeable membranes but are prevented from migrating by the cationic permeable membranes. Only ionic species are separated by this method, whereas reverse osmosis can deal with nonionic species. The advantages and disadvantages of reverse osmosis are shared by electro dialysis. 

These facts shift cost estimation to much safer side, resulting into over-investment, which may reduce the advantage of reverse osmosis process over other processes. For the fiirther prosper of reverse osmosis, we definetely need more accurate and easier method to predict membrane life which may be determined by decrease in either flux through it or separation of solute. 

Iodine has had limited application for disinfection of swimming pools [7] and small public water supplies [8]. One application in a reverse osmosis system has also been reported by Turby and Watkins [9]. Advantages of iodine are greater stability than chlorine, lower residual requirement, and diminished chemical reactivity toward dissolved organic compounds. 

The freeze concentration process is based on the partial solidification of water into ice in a fluid food product followed by the removal of the solid ice phase from the concentrated liquid phase. This process has some inherent advantages over evaporation and reverse osmosis for concentrating fluid foods as well as other process streams (1). One advantage is that essentially none... 

This technology removes dissolved metals from liquid wastes at a lower cost then other treatment options, such as precipitation followed by clarification and conventional filtration, ion exchange, reverse osmosis, and electrolysis. An advantage of the DuPont/Oberlin microfiltration technology is that it produces a dry, stabilized cake that can be landfiUed when used in conjunction with a filter aid/cake stabilizing agent. 

Figure Five (5) illustrates reverse osmosis which typically separates materials less than. 0001 microns (10 angstroms in size). Reverse osmosis offers the added advantage of rejecting ionic materials which are normally small enough to pass through the pores of the membrane. As with ultrafiltration, reverse osmosis is used to remove dissolved materials.

The use of sidestream sand filters or self-cleaning filters may be advantageous in reducing the level of suspended solids to help maintain clean waterside surfaces. If the size of the cooling system and the extent of the problem justifies it, blending with better quality water supplies or treatment of part of the makeup water volume by reverse osmosis (RO) may prove economically viable. 

Cellulose acetate was the first high-performance reverse osmosis membrane material discovered. The flux and rejection of cellulose acetate membranes have now been surpassed by interfacial composite membranes. However, cellulose acetate membranes still maintain a small fraction of the market because they are easy to make, mechanically tough, and resistant to degradation by chlorine and other oxidants, a problem with interfacial composite membranes. Cellulose acetate membranes can tolerate up to 1 ppm chlorine, so chlorination can be used to sterilize the feed water, a major advantage with feed streams having significant bacterial loading. 

A second potential application is pressure-driven desalination. When a pressure difference is applied across the membrane, the concentrated ionic groups in the ion exchange domains are swept through the membrane, producing a salt-enriched permeate on the low-pressure side. This process, usually called piezodialysis, has a number of conceptual advantages over the alternative, conventional reverse osmosis, because the minor component (salt), not the major component (water), permeates the membrane. 

Membrane distillation offers a number of advantages over alternative pressure-driven processes such as reverse osmosis. Because the process is driven by temperature gradients, low-grade waste heat can be used and expensive high-pressure pumps are not required. Membrane fluxes are comparable to reverse osmosis fluxes, so membrane areas are not excessive. Finally, the process is still effective with slightly reduced fluxes even for very concentrated solutions. This is an advantage over reverse osmosis, in which the feed solution osmotic pressure places a practical limit on the concentration of a salt in the feed solution to be processed. 

It should be noted that the electric load of a desalination unit is a deferrable one (/. < . it does not have to met by the overall power system at a specific time), which is a significant advantage in the design of the autonomous power system, since reverse osmosis units can produce potable water during periods when the other electric loads are generally low and without having to oversize the whole power system. 

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