A ﬁlter medium is any material that, under the operating conditions of the ﬁlter , is permeable to one or more components of a mixture, solution or suspension, and is impermeable to the remaining components.
The retained components, the ones to which the medium is impermeable, may be particles of solid, droplets of liquid, colloidal material, or molecular or ionic species in solution. While the permeate will normally be the suspending ﬂuid or solvent, possibly together with some of the other components.
It is true to say that any material that is porous or made into a porous structure, whether the pores are the size smaller than a micrometre, can serve as a ﬁlter medium. However, as far as is reasonable, a ﬁlter medium should be strong, ﬂexible, resistant to corrosion and abrasion, easily manipulated into the required shapes and capable of being made with a range of porosities.
- ABSORBENT, ADSORBENT AND BIOLOGICAL FILTER MEDIA:
Absorbent media : An absorbent material is akin to a sponge in that it can draw ﬂuid into itself and retain this ﬂuid within its structure, and the ﬂuid can only then desorb by a change in phase. In this sense, it can act as a ﬁlter by removing liquid droplets, for example, provided that they wet the absorbent. Thus, an untreated paper, being an absorbent material, could ﬁlter out water droplets from an air stream. Natural ﬁbres, such as wool and cotton, and the felts made from them, are also absorbent materials, but the use of such absorbent media purely as absorbent ﬁlters is very limited.
Adsorbent media : Adsorbent media are widely used for the removal of odours, smoke, fumes etc., in a wide range of applications from domestic through to air-conditioning plants and to industrial fume removal. Industrially, adsorbent ﬁlters are used for the removal of odours from oils, and of odours and tastes from foodstuffs and beverages. The adsorbent properties of the medium means that it removes dissolved as well as undissolved contaminants, the medium being chosen accordingly.
Biological ﬁlters: There is another group of equipment to which the word ‘ﬁlter’ is attached in their name that have a prime function that is not the act of ﬁ ltration, but in which ﬁ ltration does play a part. These are the biological or trickle ﬁ lters much used in the processing of water and wastewater.
VARIOUS PAPER AND FABRICS MEDIA:
- Paper media:
- Filter sheets
- Woven fabrics:
- Woven yarn fabrics
- Synthetic monoﬁlament fabrics
- Nonwoven materials:
- Wool resin media
- Needle felts
- Melt spun materials
- Bonded porous media:
- Inorganic materials