A Experiment On Water Desalination Essays

A Experiment On Water Desalination Essays

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Water desalination is the process of removing salts and minerals from water that has a high concentration of salt dissolved in it, and can therefore not be consumed as drinking water. Desalination of saline water can be achieved by a technique known as reverse osmosis. In osmosis the net movement of solvent molecules occurs from an area of low solute concentration to a more concentrated one through a semi-permeable membrane to balance the concentration of solute on either side of the membrane. However, in reverse osmosis the net flow of solvent is in the opposite direction this can be achieved by applying an external pressure that is great enough to stop osmosis from occurring, this is known as the osmotic pressure. If a pressure greater than the osmotic pressure is applied to the system then the flow of solvent molecules can be reversed and flow in the opposite direction, from a more concentrated solution to a more dilute one. This process can be related to desalination, brackish water is fed into the desalination plant and an external pressure greater than the osmotic pressure of brackish water is applied. The brackish water with a high concentration of salt ions can’t pass through the partially permeable membrane, but water can pass through the membrane to the dilute solution containing very little of the salt ions. Current reverse osmosis techniques are able to remove over 99% of all contaminants1 to ensure safe drinking water.
The overall desalination process involves a range of processes such as: pre-treatment system, high pressure pump, membrane separation unit and the post-treatment system. The pre-treatment process6 is used to prevent the pores of the partially permeable membrane being clogged up by small solid particles...

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... reduces scaling. However, if too much acid is added then this can cause corrosion of the pipes or damage to the membrane so it is important to get the balance right. Antiscalants can be added in the pre-treatment stage of desalination to reduce the levels of scale production by lowering the rate of reaction 2 this means much less calcium carbonate is produced. This occurs by three similar mechanisms: threshold inhibition, crystal distortion effect and dispersancy. Threshold inhibition7 is where the antiscalant adsorbs onto the lattice of the scale and prevents large build up salts so the lattice can never grow to be too large. Crystal distortion effect changes the structure of the crystal lattice, reducing the growth rate. Dispersancy is where similar charges are placed on the salts, so that they begin to repel each other, this prevents large crystals forming.

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