Microfiltration – Ultrafiltration – Nanofiltration
3 October 2020

Reverse osmosis theory

Reverse osmosis is a natural process which consists in the passage of water through a semi-permeable membrane from a diluted saline solution to another with greater concentration to create a chemical potential equilibrium. The pressure pushing the water through the membrane is called osmotic pressure.
By applying a pressure in excess of the osmotic pressure to the solution at higher salt concentration, the process is reversed: the water molecules pass through the membrane, while the molecules of salts, the organic molecules and almost the whole microbial charge are rejected. A concentrated solution is thus obtained on one side and pure water on the other one. This process is called reverse osmosis.
Reverse osmosis (R.O.) is a membrane separation technology that is very effective in removing almost all inorganic contaminants and dissolved solids in fluids. The phenomenon of osmosis occurs when pure water flows from a dilute saline solution through a semipermeable membrane into a higher concentrated saline solution, without energy but naturally.

Reverse osmosis technologies

Compared to traditional filtration technologies reverse osmosis (RO) is a pressure-driven separation process that employs a semipermeable membrane and the principles of crossflow filtration.
A reverse osmosis membrane is a semi- permeable membrane that allows the passage of water molecules but not the majority of dissolved salts, organics, bacteria and pyrogens. However, it is necessary 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 (demineralize or deionize) water in the process, allowing pure water through while holding back the majority of contaminants, soluble and insoluble ones. The membranes for R.O. can be able to remove up to 99,8% of substances present in water, ranging from inorganic chemicals to organic and biological contaminants. For bigger R.O. plants special attention is given to its relatively operating and capital cost. The greater portion of the operating cost of a sea water R.O. plant is the power consumption and for this reason newly developed energy recovery devices are able to reduce the energy consumption to the minimum. Managing the wastewater (brine) is also a potential problem for brackish water desalination. .