filtre à plusieurs couches

CONT: Il existe également des filtres à 3 et 4 couches [...] Leur prix est plus élevé, du fait [...] des matériaux fins et lourds (grenat...) [...] L'adoption de ce type de filtre à plusieurs couches a effectivement permis l'accroissement des vitesses de filtration et des durées de cycle [...]

CONT: Mixed media filters, called ""high rate filters"", can be used at up to 6-8 gpm [feet to the minus 2 power] and achieve much deeper penetration into the bed as the particles in the surface layer are much larger.
OBS: Mixed-media: a deep-bed filtration system utilizing two or more dissimilar granular materials, e.g., anthracite, sand and garnet, blended by size and density to produce a composite filter media graded hydraulically after backwash from coarse to fine in the direction of flow.