This study reports the investigation and application of gamma proteobacteria of the Shewanella genus, Shewanella putrefaciens CN32 bacterium, applied as a prototypical dissimilative bacterium for the remediation of Au3+, Co2+ and Fe3+ ions in aqueous systems. Green chemistry principles were applied to the remediation process, i.e. no chemicals are used to treat the metal ion solutions and process where carried out at ambient temperatures. Some emphasis upon the possibility of metal recovery as metallic nanoparticles (NPs) using bacterial cells was also given. Batch assays were carried out with de-oxygenated solutions containing metal ions of relatively low concentrations (<300mg/L) and low pH (<pH 3) in the presence of bacteria cells and H2. Biosorption of all metal ions was found to be a fast process, with a good fit to Freundlich adsorption isotherms. Transmission electron microscopy analysis of assays after 24h of incubation gave significant evidence of the precipitation of zero-valent metallic gold nanoparticles (AuNPs) in the extra-cellular medium and the outer cell wall, by initially active and deactivated bacterial cells.
- Shewanella putrefaciens