Removal of Iron and Manganese from Water—Chemistry and Engineering Considerations
As two of the earth's most common transition heavy metals, iron and manganese often occur naturally in the aquatic environment as various dissolved ions. Although iron and manganese are essential elements to humans and are relatively non-toxic, dissolved iron and manganese in water often cause mild to severe aesthetic problems such as coloured water, scaling, staining and bad water tastes. Many conventional and non-conventional resources, such as groundwater and recycled water, often contain high levels of reduced iron and manganese species, namely ferrous and manganous ions. Typically, an oxidative treatment followed by filtration is employed for the removal of dissolved iron and manganese from water. The oxidants commonly used in the iron and manganese removal processes include oxygen in air, chlorine, permanganate, chlorine dioxide and ozone. Silica sand, anthracite, greensand and manganese dioxide media may be used as granular filter media. In this chapter, the chemistry of these various oxidative technologies of iron and manganese removal in water treatment, including reaction mechanisms and kinetics, as well as engineering considerations with examples of groundwater and surface water treatment are presented and discussed.