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ARSENIC REMOVAL FROM DRINKING WATER BY IRON REMOVAL PLANTS
Fields, K., A. Chen, AND L. Wang. ARSENIC REMOVAL FROM DRINKING WATER BY IRON REMOVAL PLANTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-00/086 (NTIS PB2001-104039), 2000.
This report documents a long term performance study of two iron removal water treatment plants to remove arsenic from drinking water sources. Performance information was collected from one system located in midwest for one full year and at the second system located in the farwest for nine months. The study involved the collecting of weekly water samples through each treatment train. Every fourth week, the water samples were speciated for As III and As V. The midwest plant treated a ground water having an average arsenic concentration of 21 ug/L of which about 75% was As III. The iron concentration averaged 2.3 mg/L and is removed by a manganese greensand system. The source water is aerated and chlorinated prior to treatment which oxidizes the iron and As III to As V. During the study period, the iron removal system reduced the arsenic from an average of 21 ug/L to 3 ug/L for an average of 87% removal. The iron concentration was consistently reduced to below 0.1 mg/L. Sludge samples from the plant were tested for toxicity using the TCLP test and test results met the arsenic leaching limit of 5 mg/L. The second plant treats mining tunnel water that had an average arsenic level of 49 ug/L and an iron concentration of 1.1 mg/L. Arsenic speciation tests show that about 80% of the arsenic was in the particulate form and the remaining soluble fraction (20%) was As V. The iron removal plant reduced the arsenic by 74% to 12 ug/L and the iron level by 99% to less than 0.1 mg/L. The removal data indicate that only the particulate arsenic associated with the iron was removed. The difference in arsenic removals of the two plants was attributed to the difference in the source water iron concentration with the midwest source water having about 1 mg/L more than farwest plant source water.