The reverse osmosis process occurs when a saline solution is brought into contact with a water-permeable membrane (but impermeable to dissolved solids) at a pressure higher than the osmotic pressure of the solution itself.

It is the opposite process of “direct” osmosis, which occurs naturally in the absence of external pressures on the system. When two solutions of different concentrations, contained in two separate vessels, are brought into contact through a semi-permeable membrane, a flow occurs from the lower concentration solution toward the higher concentration solution, resulting in a decrease in concentration in the latter.

A solution with a lower salt content than the starting one (permeate) passes through the membrane, while a salt-rich solution (concentrate) is formed on the outside of the membrane.

This process represents the finest water filtration technique: a method that, to date, constitutes the most convenient and safest way for the demineralization of water from various sources, increasingly replacing other treatment systems thanks to the excellent combination of superior results and low operating costs (reverse osmosis systems guarantee low energy consumption and limited chemical product usage). Furthermore, the parameters of the waste water generally fall within the limits set for discharge, thus reducing the growing problem of eluate disposal (a problem that exists, for example, for softeners and ion-exchange resin demineralizers).

To correctly design a reverse osmosis process, it is important to determine the most suitable “pre-treatment” based on the characteristics of the water to be treated, in order to ensure maximum operational continuity of the plant and reduce the frequency of cleaning. This prevents membrane clogging due to dirt and/or physical impurities, or due to the precipitation of scaling salts and/or metals, bacterial proliferation, and contact with oxidizing agents.