Reverse Osmosis Process:
Osmosis is a natural process wherein solvent/water passes through a semipermeable membrane from the side with lower solute concentration to the higher solute concentration side until equilibrium of solvent/water chemical potential is restored. To reverse the flow of water, a pressure difference greater than the osmotic pressure difference is applied. Conclusion separation of water from salt solutions becomes possible. This phenomenon is termed reverse osmosis. It is also known as hyperfiltration.
The process is generally evaluated in terms of parameters such as water flux, Jw, solute separation, R and water recovery, Y. A definitions of these parameters are provided below.
A parameter water flux, Jw, refers to the amount of permeating solvent/water per unit time per unit area of membrane.
Jw = Qp / A.t
where, Q is the quantity of permeating solvent/water per time, t, through membrane area, A. The quantity Q might be expressed on weight basis, volume basis or molar basis.
The separation of salt by membrane is commonly expressed as solute separation R, which is the fraction of salt in the feed that does not permeate through the membrane.
R = 1- Cp / Cf
where, Cp and Cf denote solute concentration in the membrane permeated stream and in the feed inlet stream, respectively.
Water recovery Y, is generally used to describe the percentage of feed water that is converted into pure water in the permeate and is calculated as follows:
Y = (qp/qf ).100
where, qp and qf denote the quantity of permeate stream and feed inlet per unit time, correspondingly.