Arsenic removal mediated by acidic pH neutralization and iron precipitation in microbial fuel cells

Abstract

High concentrations of arsenic (As) in natural waters are a growing concern worldwide. In northern Chile, fluvial systems enriched in As from natural and anthropogenic sources have been found to contain microbial communities with exoelectrogenic activity. Previous work performed with Microbial Fuel Cells (MFCs) resulted in a neutralizing microbial community developed from a consortium extracted from northern Chile. Considering that the formation of iron minerals, which have been reported as good As sorbents, would be favored by pH neutralization, the use of neutralizing MFCs could result in a sustainable alternative for Fe and As removal. In this work, we quantified the removal of As and Fe from acidic waters in air-cathode single-chamber MFCs. Our results show a removal ~80% of As and Fe and, simultaneously, a pH neutralization from ~3.7 to ~7.2. Additionally, non-MFC experiments indicate that the removal of As and Fe is dependent only on the activity of the microbial community developed during MFC operation and not on the MFC electrochemical performance. In addition, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) analysis showed spatial associations between Fe and As on the surface of cathodes, suggesting the idea that iron oxyhydroxides formation would be associated with the higher oxygen concentration near the cathodes. Powder X-ray diffraction (XRD) analysis showed the dominance of iron amorphous minerals, which may be favoring the removal of As. These results indicate that acid/metal-tolerant bacteria favor pH neutralization and consequently the removal of Fe and As by processes of surface sorption and/or As-Fe co-precipitation. Furthermore, these findings expand the possible MFC applications to the simultaneous removal of Fe and As from acidic waters, enabling its use as an energetically sustainable bioremediation alternative.