Reverse osmosis desalination process

NF has been also been studied as a potential form of pretreatment for reverse osmosis desalination processes (Hassan et al. 1998, 2000). Based on the feed water, it may be a suitable pretreatment method that allows for operation with little or even no use of antisealants. 

Microscopically the process can be considered one of reverse osmosis (Figure 1). An osmotic membrane allows the solvent, but not the solute, to pass through it. The solvent continues to pass through the membrane until the pressure difference across the membrane is equal to the osmotic pressure (350 p.s.i. for a fresh water-sea water interface). In the reverse osmosis desalinization process, a pressure greater than the osmotic pressure applied to the sea water causes fresh water to flow through the membrane from the sea water side. 

Mane PP, Park PK, Hyung H, Brown JC, and Kim JH, Modeling horon rejection in pUot- and full scale-reverse osmosis desalination processes. Journal of Membrane Science... 

Evangelista, F. (1986). Improved graphical analytical method for the design of reverse osmosis desalination plants. Ind. Eng. Chem. Process Des. Dev., 25(2), 366-375. 

Reverse osmosis membrane process, 27 637 Reverse osmosis membrane cleaning citric acid application, 6 647 Reverse-osmosis membranes, 75 811, 825 development of, 75 797 Reverse osmosis models, 27 638-639 Reverse osmosis permeators, 76 19 Reverse osmosis seawater desalination process, 26 85 Reverse osmosis systems blending in, 26 80-81 brackish and nanofiltration, 26 80-83 Reverse osmosis technology... 

Co-location of a power plant and a seawater reverse osmosis desalination plant allows for the cooling water from a neighbouring power plant to be blended with the waste from a desalination plant before discharge (Voutchkov 2004). In such a process, seawater is used as the cooling water for the condensers in a power plant. This water is then used as both the feed for the desahnation process, and for blending to dilute the concentrate from the desalination plant. 

The reverse-osmosis membrane process is considered universally as the most promising technology for brackish and seawater desalination [18]. Potential directions for reducing desalination costs may be deduced by analyzing the cost of the components. 

Although the integration of RO with other pressure-driven membrane processes has led to significant improvements in membrane-based desalination process economics, another fundamental problem is the environmental aspects of brine discharge from reverse-osmosis desalination plants. 

Various process engineering strategies have been investigated in order to have a more environmentally friendly strategy for brine disposal in reverse-osmosis desalination. 

T. Wiimicki, etal., Desalination of Copper-Mine Brackish Water by means of an Electrolysis and Reverse Osmosis Combined Process , Proc. of the 5th Int. Symp. on Fresh Water from the Sea, Athens 1976. 

At present, an afforestation system combined with reverse-osmosis desalination or other processes is not a CO2 sink but a source. 

Eor water-treatment processes such as drinking water or potable water production, reverse osmosis (desalination), nanofiltration, and ultrafiltration are mainly used. In these processes often a microfiltration stage is implemented as the first cleaning stage for the removal of dissolved organic matter, colloids and particles from the source. 

Clever M, Jordt F, Knauf R, Rabiger N, Rudebusch M, and Hilker-Scheibel R, Process water production from river water by ultrafiltration and reverse osmosis. Desalination 2000, 131, 325-336. 

Experimental measurements of RED and PRO system performance are limited. However, a recent techno-economic analysis [143] suggests where the processes possess the greatest potential. RED is most attractive when using seawater as the concentrated salt solution while PRO is most attractive for more concentrated brines. An intriguing application is the use of PRO to recover energy from the concentrated brines produced by reverse osmosis desalination. 

Types of membranes for reverse osmosis. One of the more important membranes for reverse-osmosis desalination and many other reverse-osmosis processes is the cellulose acetate membrane. The asymmetric membrane is made as a composite film in which a thin dense layer about 0.1 to 10 pm thick of extremely fine pores supported upon a much thicker (50 to 125 pm) layer of microporous sponge with little resistance to permeation. The thin, dense layer has the ability to block the passage of quite small solute molecules. In desalination the membrane rejects the salt solute and allows the solvent water to pass through. Solutes which are most effectively excluded by the cellulose acetate membrane are the salts NaCl, NaBr, CaClj, and NajSO sucrose and tetralkyl ammonium salts. The main limitations of the cellulose acetate membrane are that it can only be used mainly in aqueous solutions and that it must be used below about 60°C. 

The system for seawater desalination, tentatively based on the reverse osmosis (RO) process, will be optimized using electric load change pattern. 

Note the similarity of the above formula to the ideal gas law and also that osmotic pressure is not dependent on particle charge. This equation was derived by van t Hoff Osmotic pressure is the basis of reverse osmosis, a process commonly used to purify water. The water to be purified is placed in a chamber and put under an amount of pressure greater than the osmotic pressure exerted by the water and the solutes dissolved in it. Part of the chamber opens to a differentially permeable membrane that lets water molecules through, but not the solute particles. The osmotic pressure of ocean water is about 27 atm. Reverse osmosis desalinators use pressures around 50 atm to produce fresh water from ocean salt water. 

Mass transfer in the entry region is far from a rare event Transport in the larger blood vessels lies entirely in the entry region, and so does mass transfer in commercial reverse osmosis desalination plants and other membrane processes (see Chapter 8). Entry lengths of many meters are not uncommon, particularly for low-solute dilfusivities. The only requirement is that flow must be in the laminar regime (Re < 2(XX)). 

Consider reverse osmosis desalination in a spiral-wound module for a feed having negligible osmotic pressure. If the fractional water recovery, re, is such that the osmotic pressure of the concentration from the reverse osmosis process still has a negligible osmotic pressure vis-a-vis the liquid pressure, derive the result (7.2.44), i.e. 

The membrane processes are characterized by quite small flow channels in and through the modules. This means that adequate prefiltration must be employed, in order to ensure as long a life as possible for the final separation stage. It is not uncommon now to find, for example, an ultrafiltration plant (with its own inlet microfilters) being used as a prefilter for a reverse osmosis desalination plant, as illustrated in Figure 2.25. 

---