Membrane filter technology uses membranes built into filters as a barrier to separate mixtures of substances. The membranes allow certain molecules or particles to pass through and block others. This enables efficient water and wastewater treatment for industry, food processing and pharmaceuticals. Depending on the degree of separation of the membranes installed in the filters, a distinction is made between the following terms:
- Microfiltration (MF) Microfiltration removes particles in the range of around 0.1 to 1 micron. In general, suspended particles and large colloids are rejected, while macromolecules and dissolved solids pass through the MF membrane. Microfilters do not always consist of membranes; sintered ceramic materials can also be used.
- Ultrafiltration (UF) Ultrafiltration enables the separation of particles with a size of around 20 – up to 0.1 microns (e.g. viruses). Dissolved salts and smaller molecules pass through the membrane.
- Nanofiltration (NF) Nanofiltration uses a membrane between ultrafiltration and osmosis, which retains particles in the approximate size range of 1 nanometre. NF works in the range between UF and reverse osmosis. Organic molecules with a molecular weight of more than 200 to 400 are rejected. Dissolved salts are also retained by 20 to 98 %.
- Reverse osmosis (RO) Reverse osmosis is one of the finest filtration stages available. The reverse osmosis membrane acts as a barrier for all dissolved salts and organic and inorganic molecules with a molecular weight of more than approx. 100. Reverse osmosis can be used to obtain water of the purest quality (so-called permeate).
For industrial water treatment, several filters of different sizes are usually installed in series, with the water being forced through the filters at a pressure of 2-6 bar. While in particle filters the filtered solids are removed from the system by sporadic backwashing, in reverse osmosis the retained salts (concentrate) are continuously flushed out of the system.
Read More
Go back to
Go back to
