Basics

Reverse osmosis is a membrane separation unit. It is the forced passage of water through a membrane against the natural osmotic pressure to accomplish separation of water and ions.

Osmosis

Osmosis is a process which can be defined as a passage of liquid from weak solution to a more concentrated solution across a semi permeable membrane. The semi permeable membrane allows the passage of liquid (solvent) but does not allow solids (solutes) to pass through.

Reverse Osmosis (RO)

Application of external pressure to the salt solution side equal to osmotic pressure will also cause equilibrium. Additional pressure will raise the chemical potential of water in the salt solution and cause a solvent flow to pure water side, now at a lower chemical potential. This phenomenon is called Reverse Osmosis.