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Filtration is a separation process where a solid-liquid mixture is percolated through a porous medium (filter) which ideally screens out solid particles, letting the liquid (filtrate) through. We mainly have in-depth filtration (filtration through a granular bed) and filtration accompanied by the formation of a cake (filtration ‘through a support’). This sub-section regroups all mechanisms and laws governing filtration, means used for monitoring and controlling a cycle, and the various wash systems. Please refer to filters for a description of the main filters.

Filtration through a clarification membrane, a spin-off from the ‘filtration through a support’, is considered under membrane separation. A description of sludge filtration, including a number of techniques involving the formation of a cake, can be found in chapter heat treatment used on dewatered sludge – general comments.