1. How reverse osmosis membranes work

Reverse osmosis membranes are composed of a thin layer, or active layer, or skin, with a thickness of between 0.1 and 1.5 µm, containing micropores; this active layer is supported by one or more layers, which are both more porous and mechanically more resistant.

For example, in the case of a 3-layer composite membrane, the skin is supported by a porous medium, ensuring easy drainage, itself arranged on a support with large openings, such as a woven or non-woven fabric, guaranteeing good mechanical strength.

It is the thin layer that controls the selective passage of substances. It is widely accepted that the selectivity and permeability of reverse osmosis membranes are the result of recurring effects due to the solubility and diffusion of substances in the membrane material.

Thus, each component of the treated medium,...