Effect of groundwater quality on adsorptive iron removal

Adsorptive iron removal from groundwater involves the adsorption of iron(II) onto the surface of the filter media and the subsequent oxidation of adsorbed iron(II) in the presence of oxygen to regenerate the adsorption site for the continuation of the process. Different ions and compounds present in groundwater might influence iron(II) adsorption onto filter media. Laboratory scale batch adsorption experiments were conducted to investigate the effect of major inorganic ions present in groundwater, i.e. Mn²⁺, Ca²⁺, NH₄⁺, SO₄²⁻, Cl⁻, alkalinity and background ionic strength on the iron(II) adsorption onto new silica sand and iron oxide coated sand. Alkalinity, background ionic strength, NH₄⁺ and Cl⁻ had no significant effect on iron(II) adsorption onto both the media tested. An increase in concentration of Mn²⁺ and Ca²⁺ decreased the iron(II) adsorption onto new sand whereas an increase in iron(II) adsorption was observed when SO₄²⁻ concentration was increased. The effect of Mn²⁺, Ca²⁺ and SO₄²⁻ on iron(II) adsorption onto iron oxide coated sand, however, was minimal. This indicates that once the iron oxide coating is developed, iron(II) adsorption is not significantly hindered due to the presence of other inorganic ions in concentrations common in groundwater.