Iron and Manganese problems are generally related to groundwater since these minerals are soluble in anaerobic and acidic conditions. Iron is generally considered to exist in aqueous solutions in equilibrium with ferrous hydroxide Fe(OH)2 and ferrous bicarbonate Fe(HCO3)2. Both forms are easily oxidized to the ferric state which is non-soluble and colored.
Manganese is widely found in nature associated with shale, sandstone and alluvial deposits. Aesthetic problems occur when these minerals are oxidized by aeration, disinfecting chemicals, iron type bacteria, and strong bleach used in laundry and automatic dishwashers. Staining problems can also be caused by corrosion of iron pipes.
The simplest and most commonly used is the method of sequestering where blended phosphate is used to keep Fe and Mn in solution, followed by chlorination to neutralize hydrogen sulfide. Sequestration is a chemical reaction between a chelating chemical and hardness or metal ions in which soluble and stable complexes are formed. True sequestration is a stoichiometric (meaning molecule for molecule) property. Scale, Fe, and Mn control in potable water is achieved with small threshold levels of 1-4 PPM of polyphosphates.
The pilot study will look at the effectiveness and feasibility of sequestering with polyphosphate followed by chlorination.