Distribution of As trapping along a ZVI/sand bed reactor

•Arsenic sorption has been studied in a ZVI/sand column for two residence times.•A heterogeneous arsenic distribution was observed along the ZVI/sand column.•A very high trapping capacity, 170 mg(As) g−1(Fe), was found at the reactor inlet.•The reactivity of ZVI byproducts towards arsenic decreased over time.

Zero-valent iron (ZVI) based reactors are widely used to remove arsenic from water and have been extensively studied, though typically by considering just the inlet and outlet arsenic concentrations. This paper presents the arsenic distribution inside an aerated bed reactor filled with a ZVI/sand support. The removal performance was evaluated through both the classical monitoring of arsenic concentrations and an analysis of the support upon completion of the experiment. Both types of analyses were performed not only at the column inlet and outlet but also at various intermediate sampling points in order to highlight the different behavior encountered along the column. The Thomas model was applied to simulate the breakthrough curves and determine sorption constants. These distinct approaches yielded similar results: while the iron distribution remained homogeneous from one approach to the next, the arsenic removal was five to six times higher at the inlet to the bed reactor than in the final ZVI/sand layer, reaching 170 mg(As) g−1(Fe). The influence of residence time was also studied, revealing that a higher arsenic load in the column led to greater retention within the first column layers.

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