In-situ groundwater treatment for arsenic removal: laboratory pilot scale study with 3-D tank packed porous media as subsurface

Abstract

ABSTRACT The ex-situ treatment of arsenic is widely adopted; however, there are emerging concerns related to system maintenance, material replacement, and waste generation. There is a scope to explore in-situ arsenite [As (III)] remediation in the aquifers. The main objective of this study is to evaluate the performance of in-situ synthesised FeS in immobilising As (III) in the natural groundwater when transported through a three-dimensional (3-D) porous media system. In this study, a 3-D tank of 0.50 m × 0.30 m × 0.30 m (L × W × H) was packed with natural sand to represent the subsurface porous media system. The homogeneous packing and uniform flow were ensured before synthesising FeS in-situ, where a total of 1.5 pore volumes (PVs) of 20 mM sodium sulfide (Na2S) and 20 mM ferrous sulfate (FeSO4) reagent solutions were injected alternatively into the pre-saturated porous media. Finally, 300 ± 15 μg/L of As (III) spiked natural groundwater was passed through the porous media, and the samples were collected through several sampling ports for analysing for total As and Fe. The result suggests that the concentration of As (III) reaches below 11 μg/L within 644 min (4 PVs) of injection of reagents. Furthermore, almost 88.4% of As (III) get immobilised after passing 31 PVs of contaminated water. In brief, almost 406 L of As contaminated groundwater can be treated by injecting 21 L of reagents with a reagent-to-treated water ratio of 1:20.