Fate of Arsenate Adsorbed on Nano-TiO2 in the Presence of Sulfate Reducing Bacteria

Abstract

Arsenic removal using nanomaterials has attracted increasing attention worldwide, whereas the potential release of As from spent nanomaterials to groundwater in reducing environments is presently underappreciated. This research investigated the fate of As(V) adsorbed on nano-TiO2 in the presence of sulfate reducing bacteria (SRB) Desulfovibrio vulgaris strains DP4 and ATCC 7757. The incubation results demonstrated that As(V) was desorbed from nano TiO2, and subsequently reduced to As(III) in aqueous solution. The release of adsorbed As(V) was two to three times higher in biotic samples than that in abiotic controls. Reduction of As(V) to As(III) in biotic samples was coupled with the conversion of sulfate to sulfide, while no As(III) was observed in abiotic controls. STXM results provided the direct evidence of appreciable As(III) and As(V) on TiO2. XANES analysis indicated that As(V) was the predominant species for three As loads of 150, 300, and 5700 mg/g, whereas 15-28% As precipitated as orpiment for a high As load of 5700 mg/g. In spite of orpiment formation, As mobilized in higher amounts in the SRB presence than in abiotic controls, highlighting the key role of SRB in the fate of As in the presence of nanomaterials.