Reversed osmosis (RO)

Reversed osmosis (called RO) is the part of the process where dissolved contaminations, such as salts and other substances, is separated from the water. Pre-treatment of the water is vital for reverse osmosis.

It  is a pressure-driven process in which the contaminated water is pumped at high speed and relatively high pressure parallel to a membrane surface. The membranes used in this process is spiral wound membrane elements. That means that a large surface of membrane has been wound around a compact element in order to create an membrane with a low mass. One or several of these elements are placed in a tank allowing the water to circulate around it and hence separate the dissolved contaminations from the water. The membrane separates up to 99% of dissolved salts and up to 90% of COD.

The contaminants are trapped by the membrane and are  concentrated in a process tank. The pressure in the tank can vary from 6-60 bars depending on the levels of salt and the desirable degree of reconcentration.


  • A membrane is a selective barrier that allows some substances to pass through it but not others, and is used to separate two differens kinds of fluids. When used on our process, it means that dissolved salts and other substances can be captured and separated from the water.
  • Reconcentration is a method used to increase the level of concentration of compounds in a fluid. In this case it indicates the lever of dissolved salts and substances being removed from the water.
  • COD means Chemical Oxygen Demand and measures the complete chemical decomposition of organic materia in water.