2.6.
Bed depth
There is no minimum or maximum bed depth, but filtration performance will improve with increasing bed
depth. For pressure filters a typical bed depth ranges from 1m to 1.4m, for RGF filters 0.5 to 2.0m.
2.7.
Grades
AFM® is provided in 4 different grades, just like a sand filter you start off with the largest grade on the
base of the filter and build up the bed to the finest grade. The ratio of grain sizes in a filter is a function of
the filter design. Generic examples are provided in this document.
2.8.
Carbon
Anthracite may be used with AFM® but there will be fewer occasions where it will be required in
comparison to sand. Activated carbon, granular and powdered can also be used with AFM® to aid in the
removal of dissolved organics.
2.9.
Flocculants and Coagulants
AFM® carries a permanent surface negative charge and works well with cationic coagulants and
flocculants that have a positive charge. There are no restrictions on the use of AFM®; the product may be
used with the following generic products;
• Ferric coagulants and flocculants.
• Aluminium coagulants and flocculants.
• Polyamide and other polyelectrolytes.
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Page 9 of 44
Figure 1: Dryden Aqua quality control and DNA crypto Laboratory. There are three
laboratories in the factory, one for water and two for glass analysis