Typically, there are two types of filtration when we think of membrane treatment. Frontal filtration or classical filtration and tangential filtration.
The Frontal Flow
Frontal filtration consists of the application of a pressure perpendicular to the filtering media. This type of flow is less and less used since the accumulation of contaminants on the walls of the membranes is very problematic since the more the membranes clog, the more the flow of permeate decreases and the internal pressure increases.
Tangential Flow
Contrary to the first type of flow, in this one, the pressure is exerted parallel to the membrane. It is thanks to a pressure gradient that the liquid crosses the membrane.
This is the type of filtration most often found today. It is used in reverse osmosis, nanofiltration, ultrafiltration and many other systems.
The pressure gradient allowing the treatment of the fluid is caused by shear stresses created by turbulence in the membranes.
To return briefly to the illustration showing the tangential flow, it is important to understand that the membranes have cylindrical shapes and are made of many layers.
This means that the water does not flow linearly through the membrane, but rather in a circular pattern.
Crossflow filtration is increasingly used because it offers significant advantages over direct filtration. These include better circulation of contaminants in the membranes, which drastically reduces membrane fouling.
