Fate of arsenate adsorbed on nano-titanium dioxide with sulfate reducing bacteria

摘要

Arsenic (As) 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. To investigate the fate of As (V) adsorbed on nano- titanium dioxide (TiO_2) in the presence of Sulfate Reducing Bacteria (SRB) Desulfovibrio vulgaris (ATCC 7757) and Desulfovibrio vulgaris DP4, multiple complimentary techniques were employed including batch incubation tests, synchrotron-based X-ray Scanning Transmission X-ray Microscopy (STXM) and X-ray Absorption Near Edge Structure (XANES) spectroscopy. The incubation results demonstrated that As (V) was desorbed from nano-TiO_2, and subsequently reduced to As (III) in aqueous solution. Reduction of As (V) to As (III) was coupled to the conversion of sulfate to sulfide and lactate to acetate. STXM results revealed that As (V) reduction also occurred on the TiO_2 surface. The release of adsorbed As (V) was promoted substantially by SRB relative to abiotic controls. XANES analysis at the end of 98 d incubation indicated that As (V) was the predominant species for As loads of 150-300 mg/g, while 15-28% As precipitated as orpiment for a high As load of 5700 mg/g. The insight gained from this study furthers our understanding of the key role of SRB in the fate of As adsorbed at the mineral-water interface.