Reverse Osmosis

Reverse osmosis is one of the so-called membrane processes, which is based on reversing the natural process of osmosis. Osmosis is a concentration equalization via a semipermeable membrane (= membrane that is only permeable to pure water and dissolved gases): if there is water with different salt concentrations on the two sides of the semipermeable membrane , the water molecules migrate from the side with less salt to the side with more salt. The more saline solution is diluted, whereby   a pressure difference builds up, the so-called osmotic pressure.

If a pressure higher than the osmotic pressure is applied on the salt-rich side, the process is reversed. The water molecules from the salt-rich side are pushed through the membrane and get to the low-salt side. The low-salt water that passes through the membranes is called permeate. The salt-rich water content flowing transversely to the membrane is referred to as concentrate.

The average pore diameter of reverse osmosis membranes is about 0.5 nm to 1 nm and is therefore only slightly larger than the diameter of a water molecule. This can also be used to separate ions and dissolved salts. Depending on the application, the required operating pressure is approximately 5 – 100 bar.

Classification of separation processes and water ingredients


  • Desalination and partial desalination for various industrial and commercial applications
  • Boiler feed water and cooling water treatment
  • Drinking water treatment: desalination of seawater and brackish water, partial desalination of well water, e.g. for the removal of heavy metals, nitrate, sulfate, fluoride, boron, organic impurities, etc.