Basic Principle of Reverse Osmosis
We have often heard people talk about reverse osmosis and its importance in the water desalination process, but what is this process and what is its origin?
Osmosis is a natural phenomenon that consists of a solvent (for example, water) passing through a membrane, that is, a barrier that only allows the solvent to pass through and not solutes or salts that this might contain (figure a and b).
” Osmotic pressure takes place naturally and spontaneously.
Let’s take for example a container. We divide it with a membrane or semipermeable barrier so that there’s no type of contact between the two parts of the container. Now we put distilled water on one side of the membrane and, on the other, water with some kind of dissolved solute (salt, sugar, etc.) so that both are at the same level. As time passes, we will note that the level of the container with distilled water has dropped by the same amount that the level in the container with salt (figure b) has gone up, owing to the passage of water, and only water, through the membrane. This height difference generates a pressure difference that is known as osmotic pressure , which takes place naturally and spontaneously.
” Currently, reverse osmosis technology desalinates at a lower energy cost per cubic meter of water.
If, however, you want to facilitate the flow in the opposite direction (from the more concentrated solution to the most diluted), it is necessary to apply hydraulic pressure (Force P) which has to overcome the osmotic pressure and the natural flow of the water through the membrane (figure c and d). Specifically, this is the phenomenon that takes place, for example, in a desalination plant where salt-free water is obtained by applying pressure to it, causing it to pass through the semipermeable membrane.
In broad strokes, this is the basic principle of reverse osmosis, which is a mature technology that currently desalinates at a lower energy cost per cubic meter of water, and which only needs electrical energy to work.