Environ. Sci. Technol. 2007, 41, 1053
Response to Comment on “Arsenic Removal from Groundwater by Household Sand Filters: Comparative Field Study, Model Calculations, and Health Benefits” We appreciate the comments made by Blaney and co-authors (1) highlighting their important contribution in providing thousands of people in West Bengal with drinking water that is treated for arsenic removal in community-based activated alumina units. Operation and performance of these units are documented in a publication published by Sarkar et al. (2). The primary comment of subject (1) refers to a remark made in the introduction of our recent article (3). We therein state: “There is an urgent need for simple and efficient As removal techniques on the household level. Ion exchange, activated alumina, reverse osmosis, membrane filtration, modified coagulation/filtration, and enhanced lime softening are water treatment technologies for As removal recommended by the USEPA. However, none of these technologies are currently applied on a broad scale in developing countries because they require sophisticated technical systems and are therefore unpractical in low income regions.” Correspondingly, our work focused on the performance and applicability of point-of-use sand filters for arsenic removal that are constructed, operated, and maintained by each individual family on their private home premises. This is a considerably different situation which cannot be compared to the community based approach referred to in the comment (1). We evaluated sand filters in Vietnam where millions of people are using arsenic-burdened groundwater for daily drinking water needs (4, 5). People in this area prefer to have a drinking water supply in their own houses. We showed that household sand filters, which use locally available sand and operate without chemicals, can achieve average arsenic removal rates of 80% in groundwater. Additionally, analyses of hair samples verified that people consuming this sandfiltered water lowered their arsenic body burden to physiologically safe levels. The concentration of dissolved iron in groundwater is the decisive factor for the removal of arsenic. The easily observable removal of iron from the pumped water makes the effect of a sand filter immediately recognizable even to people who are not aware of the arsenic problem. Regarding the use of activated alumina (AA), Blaney et al. in their comment do not mention that (i) the AA units are periodically regenerated with 175 L of 4% NaOH and 150 L of 1% HCl (2), (ii) AA must eventually be replaced after a certain lifetime, and, (iii) monitoring of arsenic levels in the unit outlet is applied (2). Hence, unlike the sand filters described in our publication (3), AA requires chemicals and presumably demands well-trained people to properly conduct such maintenance. Besides, 10% of iron seems to pass the AA unit while the household sand filters remove g99%. The second issue addressed by Blaney et al. probably arises from misreading of the section entitled “Model Calculations”
10.1021/es062798d CCC: $37.00 Published on Web 12/30/2006
2007 American Chemical Society
in our paper. We have exclusively modeled passive coprecipitation (but not sand filters) of arsenic to freshly precipitated HFO using sorption constants derived from laboratory experiments (6), but we did by no means state that “birnessite might be responsible for greater arsenic removal with sand filters than with coprecipitation.” In fact, the particular paragraphs compare coprecipitation efficiencies determined in real groundwater in the field with coprecipitation experiments performed in the laboratory in artificial groundwater. Concerning the third point, we generally agree that community-based arsenic removal providing drinking water for some 100 families has the advantage of concentrating arsenic-burdened sludge in one confined place, where its disposal can better be secured than in individual households.
Literature Cited (1) Blaney, L.; Sarkar, S.; SenGupta, A. K. Comment on “Arsenic Removal from Groundwater by Household Sand Filters: Comparative Field Study, Model Calculations, and Health Benefits”. Environ. Sci. Technol. 2007, 41, 1051-1052. (2) Sarkar, S.; Gupta, A.; Biswas, R. K.; Deb, A. K.; Greenleaf, J. E.; SenGupta, A. K. Well-head arsenic removal units in remote villages of Indian subcontinent: Field results and performance evaluation. Water Res. 2005, 39 (10), 2196-2006. (3) Berg, M.; Luzi, S.; Trang, P. T. K.; Viet, P. H.; Giger, W.; Stu ¨ ben, D. Arsenic Removal from Groundwater by Household Sand Filters: Comparative Field Study, Model Calculations, and Health Benefits. Environ. Sci. Technol. 2006, 40, 5567-5573. (4) Berg, M.; Tran, H. C.; Nguyen, T. C.; Pham, H. V.; Schertenleib, R.; Giger, W. Arsenic Contamination of Groundwater and Drinking Water in Vietnam: A Human Health Threat. Environ. Sci. Technol. 2001, 35, 2621-2626. (5) Trang, P. T. K.; Berg, M.; Viet, P. V.; Mui, N. V.; van der Meer, J. R. Bacterial Bioassay for Rapid and Accurate Analysis of Arsenic in Highly Variable Groundwater Samples. Environ. Sci. Technol. 2005, 39, 7625-7630. (6) Roberts, L. C.; Hug, S. J.; Ruettimann, T.; Billah, M.; Khan, A. W.; Rahman, M. T. Arsenic removal with iron(II) and iron(III) waters with high silicate and phosphate concentrations. Environ. Sci. Technol. 2004, 38, 307-315.
Michael Berg,* Samuel Luzi, and Walter Giger Eawag, Swiss Federal Institute of Aquatic Science and Technology Ueberlandstrasse 133, 8600 Du ¨ bendorf, Switzerland
Pham Thi Kim Trang and Pham Hung Viet Center for Environmental Technology and Sustainable Development (CETASD) Hanoi University of Science 334 Nguyen Trai, Hanoi, Vietnam
Doris Stu1 ben Institute for Mineralogy and Geochemistry University of Karlsruhe Kaiserstrasse 12, D-76128 Karlsruhe, Germany ES062798D
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