How desalination of seawater for use as drinking water relates to the principles of osmosis - Essay Example

The process utilizes the principle of reverse osmosis and has its own share of advantages and disadvantages. Description and Evaluation Osmosis is defined as “the passage or diffusion of water or other solvents through a semipermeable membrane that blocks the passage of dissolved solutes” (Kershner, 2012). Technically, water moves from an area of less solute concentration to that of greater solute concentration, because water seeks equilibrium and thus seeks to make the concentration of the area with greater solute more or less equal.

It does so through osmosis and water only stops moving once balance is attained or until equal osmotic pressure is reached. This is the state where there is no more movement by solvent. The desalination of water is not osmosis but rather the opposite of it: reverse osmosis (Kershner, 2012). In the case of reverse osmosis, there is movement of solvent molecules through a semipermeable membrane from an area of greater solute concentration to that of less solute concentration, or simply the movement of the solvent away from where solute concentration is relatively higher. . Applying pressure to saltwater to pass through the semipermeable membrane will make the solvent or water component to pass through but not the relatively bigger particles of salt.

Thus, one has salt on one side of the semipermeable membrane and freshwater on the other (Kershner, 2012). See Figure 1 for the schematic diagram of the reverse osmosis desalination plant. Figure 1. Schematic representation of a Reverse Osmosis Desalination Plant Source: http://freshlysqueezedwater.org.uk/waterarticle_reverseosmosis.php The reverse osmosis system includes several features. One of these is the type of semipermeable membrane used, upon which the percentage of tap water impurities removed depends.

Cellulose Tri-Acetate, or CTA, membranes possess a removal rate of around 88 to 94% of tap water impurities. Thin Film Composite, or TFC, membranes remove around 94 to 98% of all solids, and Hi-S membranes are responsible for the elimination of 97.5 to 99% of all impurities especially fine silicates (FAQs: Reverse Osmosis Water, 2013). Moreover, the three main components of the system include the high pressure pump, the energy recovery device and the reverse osmosis membranes. The high pressure pump is responsible for providing the pressure needed for seawater in order for it to move from an area of high solute or salt concentration to an area of lower solute concentration.

Depending on the salinity and temperature of the seawater, the amount of pressure provided by the high pressure pump ranges from 55 to 85 bars. The pressure then creates not only the movement of the flow of concentrate, but also energy. The energy recovery devices are then responsible for the reuse of the energy coming from the flow of the