Advances in the treatment of arsenic-contaminated groundwater by the adsorption onto iron-coated cork granulates on fixed-bed column

Abstract

Iron-coated cork granulates (ICG) are an emerging adsorbent successfully tested in continuous mode to remove arsenic and other oxyanions from water. Novel adsorbents are reported in the literature to show good arsenic adsorption capacities in aqueous solution; however, many fail to reach WHO limits for drinking water when treating natural water with a complex matrix. The present study investigates the performance of ICG on arsenic adsorption using different groundwater (GW) matrices, from wells in Portugal (pH 6.95 ± 0.01, NO₃⁻ = 30 mg L⁻¹, Cl⁻ = 20.4 mg L⁻¹, PO₄³⁻ = 0.12 mg L⁻¹) and The Netherlands (pH = 7.4 ± 0.1, NO₃⁻ < 0.27 mg L⁻¹, Cl⁻ = 1097 mg L⁻¹, PO₄³⁻ = 0.502 mg L⁻¹). Groundwater (As-spiked or not) was treated in lab-scale fixed-bed columns from initial concentrations (11–300 μg L⁻¹) to levels below the arsenic WHO guideline and European Union Directive 2020/2184 of 10 μg L⁻¹. The effect of an oxidation-filtration pretreatment was also investigated.

The ICG presented good performance when using real groundwater as feed across a wide range of arsenic concentrations. In all cases, the WHO guidelines and the European Commission's limit for arsenic in drinking water could be reached. The ICG performed better in the GW matrix from The Netherlands than that from Portugal. That could be attributed to the elevated concentrations of nitrate in the Portuguese matrix, which might be more competitive with the arsenic oxyanions for the ferric sites in the adsorbent, compared to the more abundant chloride in the Dutch matrix. Moreover, the pretreatment using the aeration/sand filter reactor improved the arsenic removal in the Dutch matrix. It reached values of breakthrough time, treated volume at breakthrough and bed volumes at breakthrough of 39 ± 1 h, 11.7 ± 0.4 L, 202 ± 6, respectively, for an initial concentration of 0.30 ± 0.04 mg L⁻¹. This study showed that the use of low-cost, environmentally friendly iron-coated cork granulates to remove arsenic from groundwater is feasible at different concentrations in different water matrices.