AWWA JAW46109

A simplified isotherm is described that can predict the extent of arsenate removal at drinking water utilities practicing coagulation or iron manganese (Fe-Mn) removal. If all possible sources of particulate iron and aluminum hydroxide present in the system are accounted for, the model predicts arsenic (As) removal to within plus or minus 13 percent (90 percent confidence) for Fe coagulation at pH 6.5-8 and alum coagulation at pH < 7.6. Analysis of full scale treatment data suggests that colloidal aluminum (Al) flocs with sorbed arsenate [As(V)] may pass through filters, thereby decreasing overall As removal efficiency. Thus, Al solubility and particle stability must be minimized to improve As removal. If stability and solubility of aluminum hydroxide flocs are not a problem, alum and Fe coagulants have nearly equal capacity for sorbing As(V). Survey results also demonstrate the importance of particulate As. Includes 23 references, tables, figures.