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Dynamics of arsenic adsorption in the targeted arsenic-safe aquifers in Matlab, south-eastern Bangladesh: Insight from experimental studies |
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| Authors: | Clare Robinson Mattias von Brömssen Prosun BhattacharyaSara Häller Annelie BivénMohammed Hossain Gunnar JacksKazi Matin Ahmed M Aziz HasanRoger Thunvik |
| Institution: | a Department of Civil and Environmental Engineering, University of Western Ontario, London, Canada N6A 5B9 b NGO Forum for Drinking Water Supply and Sanitation, Lalmatia, Dhaka 1207, Bangladesh c KTH-International Groundwater Arsenic Research Group, Department of Land and Water Resources Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden d Ramböll Sweden AB, Box 4205, SE-102 65 Stockholm, Sweden e Department of Geology, University of Dhaka, Dhaka 1000, Bangladesh |
| Abstract: | Targeting shallow low-As aquifers based on sediment colour may be a viable solution for supplying As-safe drinking water to rural communities in some regions of Bangladesh and West Bengal in India. The sustainability of this solution with regard to the long-term risk of As-safe oxidized aquifers becoming enriched with As needs to be assessed. This study focuses on the adsorption behaviour of shallow oxidized sediments from Matlab Region, Bangladesh, and their capacity to attenuate As if cross-contamination of the oxidized aquifers occurs. Water quality analyses of samples collected from 20 tube-wells in the region indicate that while there may be some seasonal variability, the groundwater chemistry in the reduced and oxidized aquifers was relatively stable from 2004 to 2009. Although sediment extractions indicate a relatively low amount of As in the oxidized sediments, below 2.5 mg kg−1, batch isotherm experiments show that the sediments have a high capacity to adsorb As. Simulations using a surface complexation model that considers adsorption to amorphous Fe(III) oxide minerals only, under-predict the experimental isotherms. This suggests that a large proportion of the adsorption sites in the oxidized sediments may be associated with crystalline Fe(III) oxides, Mn(IV) and Al(III) oxides, and clay minerals. Replicate breakthrough column experiments conducted with lactose added to the influent solution demonstrate that the high adsorption capacity of the oxidized sediments may be reduced if water drawn down into the oxidized aquifers contains high levels of electron donors such as reactive dissolved organic C. |
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