• Manganese oxidation requires aggressive aeration and an additional oxidising agent, such as
hypochlorite, chlorine dioxide, hydrogen peroxide or ozone in order to raise the Redox potential
to 500mv +/- 25mv.
• Ferric oxidation is simple; the aeration system will more than suffice.
• Arsenic oxidation also benefits from the addition of ferric to the water. Arsenic is removed by
oxidation and co-precipitation with ferric, example 0.1 mg/l As requires up to 1 mg/l of ferric (as
ferric chloride)
AFM® filtration
Pre-treatment of the water prior to filtration by AFM® is very important. AFM® will remove the metals
and metalloid by the following mechanisms;
• Oxidation and adsorption (similar to greensands and ferric media)
• Adsorption of sub-micron metal oxide particles
• Physical filtration of most particles down to 1 micron.
Operating parameters
AFM® filtration performance will depend upon the operating parameters. It is important to use good
quality filters, we recommend filters in compliance to the German DIN standard. The follow represent the
optimum filter bed operating conditions.
range
notes
1200mm Run phase water flow 5 m/hr 10 m/hr The slower the flow rate the better the performance
Running pressures
(differential) 0.3 0.4 Do not exceed 0.4 bar differential
Back-wash water flow >45m/hr 60m/hr Back-wash for 5 minutes or until the water runs clear. Air
purge not required
Rinse phase duration 5
minutes Or until water runs
clear It takes a few minutes for the bed to stabilize after a back-
wash
Back-wash frequency / per
week 1 7 Reduce back-washing to a minimum.
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Bulk bed density 1.25 to 1
Page 34 of 44
Bed depth AFM®