Fate of Arsenic during Anaerobic Transformation of Ferrihydrite Iron Mineral in the Presence of Clostridium sp. Strain C8 and Shewanella oneidensis Strain MR-1

Abstract

Arsenic (As) is a ubiquitous and highly toxic oxyanion-forming metalloid that extensively exists in various natural environments. There have been a few studies for removal of As using iron (oxyhydr)oxides. Here, we investigated the adsorption and structural incorporation of As(III) or As(V) in the presence of ferrihydrite and Clostridium sp. strain C8 isolated from methane gas producing consortium. Results of XRD, SEM and ferrozine assay showed that biogenic lepidocrocite (γ-FeOOH) was produced through a low-level iron reduction process in the presence of As, whereas hematite (Fe2O3) was produced in the absence of As. It is assumed that negatively charged arsenate (H2AsO4- and HAsO42-) or neutral species arsenite (H3AsO3) can be adsorbed on the surface of ferrihydrite nanoparticles, inhibiting bacterial iron reduction during the incubation time, and facilitating the formation of lath-shaped lepidocrocite crystals in the presence of As under anoxic conditions. In addition, sequential chemical extraction indicated that the amount of incorporated As into the lepidocrocite crystal structure was increased to 53.4% for As(III) and 44.4% for As(V) in the presence of Clostridium sp. strain C8. Without the bacterial inoculation, the amount of incorporated As was slightly decreased to 50.3% and 38.4% for As(III) and As(V), respectively. In overall, the incorporation of As(III) into the lepidocrocite is more favorable than that of As(V) in the presence of Clostridium sp. strain C8. Additionally, As remobilization from the biogenic lepidocrocite was hardly observed up to 43 d after incubation of Shewanella oneidensis strain MR-1 although there is a possibility of resorption of arsenic on the structure surface of lepidocrocite. Therefore, the transformation of ferrihydrite to biogenic lepidocrocite can provide an efficient and cost-effective solution, thereby the As incorporation process plays an important role for bioremediation in As-contaminated environments.