AWWA JAW68771

Arsenic removal was characterized at 31 iron removal plants in Illinois representative of many similar facilities in the upper Midwest. The plants used different iron removal processes and had a wide range of arsenic, iron, and total organic carbon concentrations. Iron concentration in raw water is an important factor in arsenic removal. Removal of arsenic depends on oxidation of arsenite to arsenate, adsorption of arsenic to hydrous ferric oxide (HFO), and filtration to remove HFO and any adsorbed arsenic. In the current work, soluble arsenic concentrations were lowered by at least 75% when the iron concentration of the raw water was > 3 mg/L Fe. In both models of soluble arsenic removal developed in this research, adsorption to HFO was assumed to be the only reaction that removes arsenic from solution. A generalized double-layer model generally underpredicted arsenic removal, whereas a parametric model that was consistent with surface complexation and accounted for the effects of other adsorbing substances, fit the data fairly well. Includes 54 references, tables, figures.