How does it work?
To understand why reverse osmosis is required it is important to understand osmosis.
Osmosis is a naturally occurring process in nature, where a weaker, less concentrated saline solution will migrate to a strong saline solution with a higher concentration.
For example, if you had a container full of water with a low salt concentration and another container full of water with a high salt concentration and they were separated by a semi-permeable membrane, then the water with the lower salt concentration would begin to migrate towards the water container with the higher salt concentration.
In osmosis, water becomes more concentrated as it passes through the membrane to obtain equilibrium on both sides, however reverse osmosis, blocks contaminants from entering the less concentrated side of the membrane.
Reverse Osmosis is basically the process of Osmosis in reverse.
Whereas Osmosis occurs naturally without energy needed, to reverse the process of osmosis you need to apply energy to the more concentrated water.
You need to ‘push’ the water through the reverse osmosis membrane by applying pressure that is greater than the naturally occurring osmotic pressure in order to desalinate the water in the process, this allows the pure water through while holding back a majority of contaminants.
The pressure is produced by a high-pressure pump and leaves almost all (around 95% to 99%) of dissolved salts behind in the reject stream. The amount of pressure required depends on the salt concentration of the feed water. The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure.
The desalinated water that is demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream.