Membrane filtration includes all processes in which substances are filtered through membranes. The size of the pores determines which particles are retained and which pass through the membrane. The difference in the various filtration processes is in their pore diameter:
Micro filtration 0.5 – 0.1 µm
Ultra filtration 0.1 – 0.01 µm
Nano filtration 0.01 – 0.001 µm
Reverse osmosis 1.0 – 0.1 µm
The membranes are made of synthetics or ceramics. Depending on the design of the modules for filtration, a differentiation is made between hollow fibre membrane modules, spiral modules, tubular modules, plate modules and cushion modules. Ruland mainly uses hollow fibre and spiral modules for its filtration systems.
If microorganisms are to be filtered from liquids, this is called sterile filtration. Bacteria-proof membranes are used for sterile filtration. Sterile filtration is used for heat-sensitive liquid products such as vitamin solutions, vaccines, protein solutions, but also for wine, beer, fruit juice drinks, plasma fractionation and fermentation processes.