AMF AMF Users Manual | Page 46

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Annex 3. The removal of Arsenic, Ferric and Manganese

Manganese Mn2 + Mn4 + 50 ug / l > 80 % Ferric Fe2 + Fe3 + 200 ug / l > 95 %

AFM ® performance

Arsenic As3 + As5 + 10 ug / l > 95 % 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 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.

Oxidation;

Manganese and Arsenic are removed by co-precipitation and catalytic oxidation by Ferric. For the process to work the ferric needs to be at least 5 times higher concentration than either the arsenic or the manganese. If the concentration of ferric is sufficient, then simple aeration of the water for a period of up to 30 minutes, with co-precipitate the arsenic and manganese and the AFM ® will remove from solution.

The process is very simple and easy to reduce the arsenic concentration to less than 10ppb in a sustainable system. If the water is deficient in ferric, it may be compensated for by dosage of ferric chloride.

If ferric is not used for catalytic oxidation of Manganese or Arsenic, then an oxidising agent such as chlorine dioxide needs to be added to the water to raise the redox potential to 500mv.

Aeration

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.