Coagulation technology for arsenic removal trations of arsenic in the range of 20 to 80 µg/L, coagu- lation-filtration also would be the selected process to remove arsenic (28). Because of the afore-mentioned characteristics of water quality, adsorption processes are inefficient in the removal of arsenic. In addition, most manufacturers of sorbents do not provide regene- ration instructions. CONCLUSION The Chilean experience in removal of arsenic demon- strates that the water matrix dictates the selection of the arsenic-removal process. The coagulation process has been proven to be an effective arsenic-removal process for surface and groundwater. Moreover, it has the ad- vantage that it does not typically require excessive pre- treatment or conditioning of influents and chemicals used that are not made in Chile. The Chilean water industry has gained significant operational experience in the removal of arsenic by coagulation and will rely on achieving a residual ar- senic concentration of 10 µg/L by coagulation techno- logy through adjustment of pH and control of coagulant dose. The Chilean experience in the removal of arsenic at water-treatment plants demonstrates that the processes of coagulation/adsorption-sedimentation-filtration can remove arsenic up to the WHO-recommended stand- ards for drinking-water. These processes do not require complex pre-treatment of water, but only pre-oxidation and pH adjustment. This technology for the removal of arsenic can be simplified by eliminating the sedimenta- tion process if the conditions of water permit. The inputs of this technology—oxidizing agent, co- agulant, filtering medium—can be of local origin, and the operation of the removal system requires personnel with an intermediate level of training. The handling and disposing of the sludge generated must always be done with special precautions. ACKNOWLEDGEMENTS This paper is based on studies supported by Universi- dad de Chile and FONDEF-CONICYT through Project FONDEF 2-24. The author is grateful for the many contributions of her students, whose cooperation made these studies possible. REFERENCES 1. Sancha A. Removal of arsenic from drinking water supplies: Chile experience. Water Sup- ply 2000;18:621-5. 271 2. Sancha A. Removing arsenic from drinking water. A brief review of some lessons learned and gaps arisen in chilean water utilities. In: Chappell W, Ab- ernathy C, Calderon R, Thomas D, editors. Arsenic exposure and health effects. Amsterdam: Elsevier B.V., 2003:471-81. 3. Alonso H. Arsenic enrichment in superficial wa- ters. II. Región Northern Chile. In: Sancha A, edi- tor. Proceedings of the International Seminar on Arsenic in the Environment and Its Incidence on Health. Santiago: Universidad de Chile, 1992:101-8. 4. Borgoño J, Greiber R. Estudio epidemiológico del arsenicismo en la ciudad de Antofagasta. Rev Med- Chile 1971;99:702-9. 5. Latorre C. Estudio fisico-químico para la remoción del arsénico en el rio Toconce. Santiago: Revista Ingenieria Sanitaria 1966:12-21. 6. Sancha A. Experiencia Chilena en remoción de ar- sénico en fuentes de agua potable. Santiago: Sec- ción Ingenieria Sanitaria y Ambiental, Universidad de Chile, 1986. 44 p. (Publ 0-18). 7. Sancha A, Ruiz G. Estudio del proceso de remoción de arsénico de fuentes de agua potable empleando sales de aluminio. In: Proceedings XIX Congreso Interamericano de Ingeniería Sanitaria y Ambiental (AIDIS) Chile, Tema I Agua Potable, 1984;2:380- 410. 8. Sancha A. Full-scale application of coagulation processes for arsenic removal in Chile: a successful case study. In: Chappell W, Abernathy C, Calderon R, editors. Arsenic exposure and health effects. Amsterdam: Elsevier Sciences B.V., 1999:373-8. 9. Ruiz G, Perez O, Sancha AM. Filtración directa para el Tratamiento de Aguas Subterráneas con arsénico. In: Proceedings XXIII Congreso de la Asociación Interamericana de Ingenieria Sanitaria y Ambiental (AIDIS), La Habana: AIDIS Cuba, 1992:729-39. 10. World Health Organization. Arsenic in drinking water. Chapter VI. Safe water technology. Geneva: World Health Organization, 2002. 98 p. 11. Edwards M. Chemistry of arsenic removal dur- ing coagulation and Fe-Mn oxidation. J AWWA 1994;86:64-78. 12. Hering J, Chen P, Wilkie J, Elimelech M, Liang S. Arsenic removal by ferric chloride. J AWWA 1996;88:155-67.