Introduction to the principle of reverse osmosis

Reverse osmosis is one of the most effective water treatment methods in the existing technology. It can effectively treat salt (such as calcium, magnesium and other hardness impurities), heavy metals, and chemical residues in the water to more than 95%. RO reverse osmosis water treatment technology can be seen everywhere today, such as seawater desalination systems, electronic ultrapure water refining systems, biochemical pharmacy, kidney dialysis, cosmetics manufacturing, beverages, packaged water and even general household filtration.

What is osmosis, osmotic pressure and reverse osmosis?

A membrane that is selective to the substance that passes through is called a semipermeable membrane. Generally, thin films that can only penetrate solvents but not solutes are regarded as ideal semi-permeable membranes.

When the same volume of dilute solution (such as fresh water) and concentrated liquid (such as sea water or salt water) are placed on both sides of a container, with a semi-permeable membrane in the middle, the solvent in the dilute solution will naturally pass through the semi-permeable membrane, When the concentrated solution flows on the side, the liquid level on the concentrated solution side will be higher than the liquid level of the dilute solution by a certain height, forming a pressure difference and reaching a state of osmotic equilibrium. This pressure difference is the osmotic pressure. The size of the osmotic pressure depends on the type of the concentrate, and the concentration and temperature have nothing to do with the properties of the semipermeable membrane.

If a pressure greater than the osmotic pressure is applied on the side of the concentrated solution, the solvent in the concentrated solution will flow to the dilute solution. The flow direction of this solvent is opposite to the original permeation direction. This process is called reverse osmosis.

Reverse osmosis is a separation method that separates the solute in the solution from the solvent by the selective retention of a semi-permeable membrane under pressure. It is widely used in the separation and concentration of various liquids. In the water treatment process, impurities such as inorganic ions, bacteria, viruses, organic matter and colloids are removed from the water to obtain high-quality water.

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