Annex 3: The removal of Arsenic, Ferric and Manganese
Chemical parameter Soluble fraction Insoluble Drinking water
standard AFM® performance
Manganese Mn2+ Mn4+ 50 ug/l >80%
Ferric Fe2+ Fe3+ 200 ug/l >95%
Arsenic As3+ As5+ 10 ug/l >90%
Iron, manganese and arsenic are often found in borehole / tube wells and ground-water at varying
concentrations depending upon the geology of the ground. The process used by Dryden Aqua to remove the
chemicals is as follows;
Process
1. Oxidation reactions to convert
metals from soluble ionic form to
insoluble oxidized precipitate, pH
correction and redox correction.
2. Decantation may be required if the
concentrations are above 5 mg/l, if
not proceed to AFM® filtration
3. AFM® filtration to remove the
suspended metal oxide solids,
there will also be adsorption
reactions and surface oxidation
reactions.
Procedure
Oxidation;
This is achieved through aeration of the water. The water is aerated for a period of no less than 30
minutes. If water flow is 50 m3/hr the aeration level is 50m3/hr of air and tank volume is 25m3 of water.
Dryden Aqua manufacture fine bubble drop in air diffusers for this application.
pH;
The pH of the water should be increased to a value over pH 7.5
Redox;
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Page 33 of 44
The aeration system should increase the redox potential of the water. It is important to raise the potential
to as high a value as possible. Certainly it should be over 300mv for ferric and arsenate. Manganese
needs an additional oxidising agent to raise the potential to 500mv. A ZPM between the pump and
AFM® filters should also be fitted.