Filtration means separation only in a physical and mechanical way.
During the filtering process, mixtures (suspensions) are mechanically separated from liquids containing solids (particles or molecules).
During water treatment, the optimum filtration processes or a combination of several methods is chosen depending on the quality of the raw water as well as the specifications for purity after filtration.
Membrane filtration is a dynamic filtering process. The flow direction of the liquid or gas is here not vertically through the filter area but horizontally through membranes. By selecting a filter pore size of a membrane, the fineness of filtration, i.e., the size of the particles to be removed, can be determined.
This is used mainly in the food industry and serves as filtration technology for fluids with high murky contents (such as fruit juice, wine, etc.) but finds use in dialysis as well.
The material of the filter surface in microfiltration may be - depending on the application area - made from plastic, textile fabric or stainless steel. The filter pore size of this technique is > 0.1 µm.
Microfiltration is used, for example, to separate oil-water emulsions, biotechnology applications, or to separate colloidal oxides or hydroxides.
The filter pore size of ultrafiltration is 0.1 to 0.01 µm. Ultrafiltration is used for such applications as separating proteins, cold sterilization in the pharmacy, or for metal recovery and wastewater cleaning in the field of metallurgy.
Nanofiltration is a pressure-driven membrane processes. In contrast to reverse osmosis, nanofiltration uses lower pressures and filters with larger pore sizes. The particle size, which is retained in nanofiltration, is the size of single and divalent heavy metal ions. Nanofiltration is used, for example, for softening water and the removal of heavy metals during drinking water treatments.
Reverse osmosis or also is a pressure-driven membrane process in which pressure reverses the natural osmosis process.
It is used to treat drinking and process water, aquarium water, to produce fruit juice concentrates, and in the treatment of wastewater.