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ARSENIC REMOVAL FROM DRINKING WATER BY COAGULATION/FILTRATION AND LIME SOFTENING PLANTS
Fields, K., A. Chen, AND L. Wang. ARSENIC REMOVAL FROM DRINKING WATER BY COAGULATION/FILTRATION AND LIME SOFTENING PLANTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-00/063 (NTIS PB2001-100152), 2000.
This report documents a long term performance (one year) study of 3 water treatment plants to remove arsenic from drinking water sources. The 3 plants consisted of 2 conventional coagulation/filtration plants and 1 lime softening plant. 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. Residuals samples were also colected at each facility during a 2 month period for Toxicity Characteristic Leaching Procedures (TCLP) testing. One coagulation/filtration plant reduced the source water arsenic concentraton from about 8 ug/L to <4 ug/L (52% removal) while the second plant reduced the arsenic from about 19 ug/L to 4 ug/L (79% removal). Adsorption and coprecipitation iron and aluminum floc were believed to be the removal mechanisms. The lime softening facility reduced its source water arsenic concentration from 32 ug/L to about 16 ug/L (45% removal). Adsorption and coprecipitation with the iron that was present in the source water was concluded to be the primary removal mechanism because the plant operated at a pH of 9.6. At this pH, arsenic removal by lime softening is reported to be < 10%. Higher removal could have been likely achieved if the plant operated at a pH >11. All of the sludge samples collected at the 3 plants passed the TCLP testing limits for arsenic and therefore, were considered nonhazardous. This project was conducted to support the revision of the arsenic MCL as required by the USEPA under the 1996 SDWAA.