Removal of arsenic from contaminated groundwater by goethite adsorption in the presence of the arsenite-oxidizing bacterium Aliihoeflea sp. strain 2WW

Contamination of aquifers with As has raised great concern, because of serious risks to human health. The revised drinking water standard for arsenic imposes a 10 μg L-1 threshold limit, which has boosted research efforts to remove As efficiently. Arsenic has a high affinity for adsorption to metal oxides, with As(V) being more effectively adsorbed than As(III). Consequently the oxidation of As(III) to As(V) is a prerequisite for achieving As concentrations below the threshold. Bio-oxidation of As(III) by microorganisms has recently received attention as a sustainable alternative to the use of chemical oxidants. The aim of our work was to improve the removal of As from groundwater by oxidizing As(III) to As(V) followed by adsorption to goethite. For this purpose, we first isolated an arsenite-oxidizing bacterium, Aliihoeflea sp. strain 2WW, from a biofilm treating contaminated groundwater, and subsequently investigated the As(III) oxidation capability of this strain. The experiments were conducted in Tris-HCl 5 mM (pH 7.2) containing 200 μg L-1 of As, using As(III)-induced and non-induced resting cells. As(III) and As(V) adsorption capability of goethite was evaluated by using 4 g L-1 goethite and increasing As concentrations (25-800 μg L-1). Finally we tested the As-removal efficiency of the combined 2WW-goethite system on a synthetic contaminated water and a contaminated groundwater sample. Resting cells of an As(III)-induced culture of 2WW were able to oxidize completely 200 μg L-1 of As in 8 hours, while non-induced cells oxidized As in 24 hours. Subsequently, results from the As-adsorption experiments showed that goethite removed almost the complete 200 μg L-1 of As(V) from the solution, while for As(III) only 75% was adsorbed. Our results indicate that As(III) oxidation by Aliihoeflea sp. strain 2WW combined with goethite adsorption is an efficient approach for the removal of As from contaminated groundwater. Research funded by CARIPLO Foundation-2010-2221.