Iron and manganese are among the most common problems in industrial water supplies. Dissolved and invisible at the source, they oxidise on contact with air, producing staining, deposits in pipework, fouling of membranes and blocked nozzles downstream.
The treatment principle
Both metals are removed by converting them from soluble to insoluble form, then filtering the resulting particles. Iron in its dissolved ferrous form oxidises to ferric hydroxide, which is a filterable solid. Manganese behaves similarly but oxidises more slowly and requires higher pH and stronger oxidant.
Oxidation options
Aeration is the simplest and cheapest where iron levels are moderate, giving good results with adequate contact and settling time. Chemical oxidants act faster and handle manganese better. Hydrogen peroxide is used where a residue free oxidant is preferred, since it decomposes to water and oxygen, an approach discussed in our dosing basics article. Chlorine and permanganate are alternatives with their own residual and handling considerations.
Contact time before filtration is critical. Oxidation is not instantaneous, particularly for manganese, and filtering before the reaction completes passes dissolved metal straight through to cause problems downstream.
Filtration
Once oxidised, the precipitate is removed by media filtration. Media selection depends on loading and particle characteristics, and backwash frequency is set by pressure differential rather than a fixed calendar. Undersized filters foul quickly and drive excessive backwash water consumption.
Where activated carbon belongs
Granular activated carbon is frequently misapplied here. It is excellent for removing residual oxidant, taste, odour and organics, and it will remove some oxidised iron as a filter, but it is not an economical primary iron removal medium. Placing carbon after oxidation and filtration protects downstream equipment and removes excess oxidant. Placing it before removal loads it with iron and exhausts it prematurely, as our EBCT sizing guide explains.
Design from analysis
Start with a full water analysis: iron and manganese speciation, pH, alkalinity, organic content and any competing species. Iron bound in organic complexes behaves differently from simple dissolved iron and often defeats a standard oxidation and filtration design.
MENA Industrial Supplies supplies oxidants and activated carbon for UAE water treatment with certificates of analysis.