Arsenic/Iron Removal From Groundwater With Elevated Ammonia and Natural Organic Matter

Under the US Environmental Protection Agency's Arsenic Demonstration Program, an iron (Fe) removal process consisting of permanganate oxidation and greensand filtration was shown to be effective in removing soluble arsenic (As(III)) (24.1 microg/L on average) from Waynesville, Ill., groundwater, which also contained elevated ammonia (3.8 mg/L [as N] on average) and natural organic matter (NOM) (7.9 mg/L, on average, of total organic carbon). Chlorine was not used because it forms chloramines, which are not effective in oxidizing As(III). A permanganate dose over the stoichiometric amount was applied to overcome interference from NOM-based on jar testing conducted for this and another Fe removal system at Sauk Centre, Minn. These pressure filtration syste ms had no air contact, thus allowing simultaneous oxidation of As(III) and ferrous iron. Compliance monitoring data to date show consistently low arsenic (<4 microg/L) and Fe (<0.05 mg/L) since the commencement of system operation in July 2009.