Water components can be divided into suspended solids and dissolved solids. Solids like suspended matter and granular particles can be removed almost completely through filtration as long as particle size and specific gravity are significant enough. During filtration, water passes a porous substance (filter medium) retaining unwanted particles on the surface or inside.
The most simple filter types are (backwashable) fine filters that, for safety reasons, are mounted directly in the installation inlet pipe. If more impurities are expected, different filter media are used, depending on the filtration task (mechanical impurities; iron, manganese or chlorine removal).
Such filter media can be:
They retain flocculated suspended and turbid matter from well, surface and process water. Unlike mono-medium filters, a combination of different filter media, such as hydro-anthracite and filter gravel, enables in-depth filtration and thus a higher dirt-holding capacity. The filter's service life is extended while the operating costs diminish. Depending on the requirements, it is possible to fill multimedia filters with only one kind of filter material, such as activated carbon.
They are preferably used in open cooling circuits, where the cooling water is contaminated by pollen and dust from the environment. Consequences such as deposits, biological contamination and corrosion lead to unit malfunctions and impair proper system operation. Sand filter units that filter 5-10 % of the water system volume per hour in a separate circuit guarantee clean cooling water and smooth system operation.