• Microfiltration (MF)
• Ultrafiltration (UF)
• Nanofiltration (NF)
• Reverse osmosis (RO)

Membrane filters are purely mechanical "fine sieves".

These fine sieves consist of porous, artificially created films, so-called membranes, with precisely defined pore diameters.



Membrane function

The pore diameters define the membrane type and relate directly to the separation rates:
All substances smaller than the pores can pass through the membrane, and larger substances are held back. In the context of drinking water treatment, this unselective process is disadvantageous, as both undesired and desired minerals are partially or totally removed.

Membrane structure

The actual effective membrane layer is extremely thin and is located on the side facing the raw water.
The absolutely largest part of a visible membrane is the carrier material required for the physical structure and strength.
It is important that the pores of a membrane increase in size toward the pure water in order for the membrane to function properly. Otherwise, there is a risk of permanent blocking.



Materials

Today’s common membranes consist of plastics (e.g. polysulphone) or ceramic.

Types

A differentiation is made between the following, depending on the use and structure:

• Hollow-fibre membrane modules
• Spiral modules
• Plate modules
• Pipe modules