TY - JOUR
T1 - Exploring sustainability of aquifers based on predictive modeling of sorption characteristics of arsenic enriched Holocene sediments in Bangladesh
AU - Tauhid-Ur-Rahman, M.
AU - Mano, Akira
AU - Udo, Keiko
AU - Ishibashi, Yoshinobu
N1 - Funding Information:
The first author (MTR) is grateful to the Japan Society for the Promotion of Science (JSPS) for awarding the post-doctoral fellowship. The authors acknowledge financial support by the Grant in Aid for Scientific Research from the Japan Society for the Promotion of Science (B-18404009 and 21-09288). The authors would like to express gratitude for the technical support received from the technical staff of Tohoku University, including Mr. Takahashi and Mr. Chiba for ICP-MS analysis and Mr. Miyazaki for SEM analysis. Special thanks are also given to Prof. Hiroshi Inomata and Prof. Toshiaki Yoshioka of Tohoku University for their help with BET and XRD analyses, respectively. We deeply appreciate the meticulous reviews of the two anonymous reviewers and the guest editors Alan Fryar and Prosun Bhattacharya for their constructive comments on the earlier draft of this manuscript.
PY - 2011/4
Y1 - 2011/4
N2 - The importance of accessing safe aquifers in areas with high As is being increasingly recognized. The present study aims to investigate the sorption and mobility of As at the sediment-groundwater interface to identify a likely safe aquifer in the Holocene deposit in southwestern Bangladesh. The upper, shallow aquifer at around 18m depth, which is composed mainly of very fine, grey, reduced sand and contains 24.3μg/g As, was found to produce highly enriched groundwater (190μg/L As). In contrast, deeper sediments are composed of partly oxidized, brownish, medium sand with natural adsorbents like Fe- and Al-oxides; they contain 0.76μg/g As and impart low As concentrations to the water (4μg/L). These observations were supported by spectroscopic studies with SEM, TEM, XRD and XRF, and by adsorption, leaching, column tests and sequential extraction. A relatively high in-situ dissolution rate (Rr) of 1.42×10-16mol/m2/s was derived for the shallower aquifer from the inverse mass-balance model. The high Rr may enhance As release processes in the upper sediment. The field-based reaction rate (Kr) was extrapolated to be roughly 1.23×10-13s-1 and 6.24×10-14s-1 for the shallower and deeper aquifer, respectively, from the laboratory-obtained adsorption/desorption data. This implies that As is more reactive in the shallower aquifer. The partition coefficient for the distribution of As at the sediment-water interface (Kd-As) was found to range from 5 to 235L/kg based on in-situ, batch adsorption, and flow-through column techniques. Additionally, a parametric equation for Kd-As (R2=0.67) was obtained from the groundwater pH and the logarithm of the leachable Fe and Al concentrations in sediment. A one-dimensional finite-difference numerical model incorporating Kd and Kr showed that the shallow, leached As can be immobilized and prevented from reaching the deeper aquifer (∼150m) after 100 year by a natural filter of oxidizing sand and adsorbent minerals like Fe and Al oxides; in this scenario, 99% of the As in groundwater is reduced. The deeper aquifer appears to be an adequate source of sustainable, safe water.
AB - The importance of accessing safe aquifers in areas with high As is being increasingly recognized. The present study aims to investigate the sorption and mobility of As at the sediment-groundwater interface to identify a likely safe aquifer in the Holocene deposit in southwestern Bangladesh. The upper, shallow aquifer at around 18m depth, which is composed mainly of very fine, grey, reduced sand and contains 24.3μg/g As, was found to produce highly enriched groundwater (190μg/L As). In contrast, deeper sediments are composed of partly oxidized, brownish, medium sand with natural adsorbents like Fe- and Al-oxides; they contain 0.76μg/g As and impart low As concentrations to the water (4μg/L). These observations were supported by spectroscopic studies with SEM, TEM, XRD and XRF, and by adsorption, leaching, column tests and sequential extraction. A relatively high in-situ dissolution rate (Rr) of 1.42×10-16mol/m2/s was derived for the shallower aquifer from the inverse mass-balance model. The high Rr may enhance As release processes in the upper sediment. The field-based reaction rate (Kr) was extrapolated to be roughly 1.23×10-13s-1 and 6.24×10-14s-1 for the shallower and deeper aquifer, respectively, from the laboratory-obtained adsorption/desorption data. This implies that As is more reactive in the shallower aquifer. The partition coefficient for the distribution of As at the sediment-water interface (Kd-As) was found to range from 5 to 235L/kg based on in-situ, batch adsorption, and flow-through column techniques. Additionally, a parametric equation for Kd-As (R2=0.67) was obtained from the groundwater pH and the logarithm of the leachable Fe and Al concentrations in sediment. A one-dimensional finite-difference numerical model incorporating Kd and Kr showed that the shallow, leached As can be immobilized and prevented from reaching the deeper aquifer (∼150m) after 100 year by a natural filter of oxidizing sand and adsorbent minerals like Fe and Al oxides; in this scenario, 99% of the As in groundwater is reduced. The deeper aquifer appears to be an adequate source of sustainable, safe water.
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U2 - 10.1016/j.apgeochem.2011.01.020
DO - 10.1016/j.apgeochem.2011.01.020
M3 - Article
AN - SCOPUS:79952696491
SN - 0883-2927
VL - 26
SP - 636
EP - 647
JO - Applied Geochemistry
JF - Applied Geochemistry
IS - 4
ER -