Treating Iron Content in Water
Why treat Iron content in Water?
Iron (Fe) and Manganese (Mn) in water sources can become a serious operational issue in downstream process equipment. Depending on the concentration of the Fe and Mn in the water source, this could lead to an aesthetic (lower concentrations) or a chronic health (higher concentrations) issue when water is utilised as a potable water source. High Fe and Mn concentrations are generally not seen when dealing with surface water sources, however, exceptions can occur. High naturally occurring Fe and Mn concentrations are predominant in groundwater sources, where contact with minerals impart the elevated concentrations. Close proximity to mining activities can also impart elevated Fe and Mn concentrations to the water source.
Fe and Mn often occur together in groundwater sources, however, the Mn concentration is generally at much less elevated levels than Fe. Both Fe and Mn impart a strong metallic taste to drinking water and cause staining. Exposing the water to air/oxygen causes brownish/orange stains from the Fe precipitation and blackish stains from the Mn precipitation. Fe, however, oxidises/precipitates much more readily (i.e. at lower pH levels and lower dissolved oxygen levels) than Mn.
The Treatment Process
Treatment processes for the removal of Fe and Mn varies over a broad range of treatment options and
technologies. The various treatment options can be roughly classified as either (1) biological or (2) physio-chemical. Certain treatment options are limited to lower Fe and Mn concentrations and, depending on the concentration levels, additional treatment processes can be added when higher concentrations are evident. It is therefore critical to have a good understanding of the feed water quality, the target water quality (i.e. should the water be treated to potable standards, irrigation standards, etc.), plot-space availability, plant capacity and hydraulic demand, etc. Obtaining all relevant data would therefore enable the TWS to compile an accurate design basis from which the most cost-effective solution can be proposed.
Author – Rassie van der Westhuizen (CTO, TWS | July 2020)