Achme Water
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Iron Removal

Iron and manganese are unaesthetic parameters present mostly in groundwater, causing unwanted precipitation and color.

Iron removal is based on the precipitation of dissolved iron (Fe2+) into its oxidized form (Fe3+), as Fe(OH)3 or Fe2O3.

Iron removal by physical-chemical way consists in iron oxidation by air followed by sand filtration,
but other techniques exist as well:

Oxidation + sand filtration
(physical chemical way)
For water with pH > 7, low redox potential, low iron content (< 3mg/L)
Oxidation + sand filtration + MnO2 filter For higher iron content and/or manganese
Oxidation + green sand More efficient than sand filtration but required KMnO4 regeneration
Oxidation + Limestone contactor For acidic water with low redox potential, the limestone contactor increases aggressive water pH by binding CO2
Ion exchange Recommended for continuous process with low iron content. Not pH dependent

Oxidation can be carried out by various chemicals like chlorine, ozone but is mostly done by compressed air.

Complex bound iron and manganese, e.g. complex bound with humic acids, can be very difficult to remove. In this case oxidation with ozone can be a solution.

Manganese removal

For manganese removal only, Manganese dioxide (MnO2) is used as an adsorbent according to the following reaction:

Mn + MnO2 (s) --> 2 MnO (s)

Manganese oxides are then adsorbed on MnO2 grains. When all MnO2 has been consumed, it can be regenerated by sodium hypochlorite.

Manganese removal by physical-chemical way (aeration and sand filtration) can also be used but manganese oxidation kinetics are too slow at pH< 9.