Enhanced Natural Attenuation Mediated by Autochthonous Bacteria for Recovering Cr(Vi)-Polluted Groundwaters

The presence of Cr (VI) in groundwater, at concentrations significantly higher than legal limits, represents a widespread environmental problem. Environmental contamination is mainly related to the incorrect management of process water and byproducts coming from numerous industrial processes involving chromium. Groundwater remediation can be conveniently achieved by reducing Cr (VI) to Cr (III), since the latter is less soluble and less mobile through environmental matrices, as well as a hundredfold less toxic for living organisms than Cr(VI). Biological reduction is potentially advantageous in terms of economic and environmental sustainability, especially in the case of large volumes of water. Ubiquitous organisms, characterized by high metabolic plasticity, such as bacteria, are able to detoxify the environment surrounding the cell by reducing Cr (VI). However, these microorganisms are generally heterotrophic and need an external source of nutrients to support their growth and reproduction, especially in oligotrophic environments such as groundwater. Enhanced natural attenuation can be achieved by supplying suitable amendments that can both support bacterial biomass production and provide electrons for reductive processes. The NGS technologies applied to the 16S rDNA region can provide the structure of the native bacterial community, highlighting changes before and after treatment. This approach also allows investigating a possible amendment-driven enrichment of chromium-reducing bacteria. The capability of indigenous bacterial consortia to remediate Cr(VI)-polluted groundwater was investigated by a bioremediation test carried out at a microcosm scale. Microcosms setup was performed using deep saturated soil and groundwater collected from an industrial site in the territory of Barletta Municipality, where Cr(VI) was detected in groundwater at a concentration of about 140 µg L -1 . The effectiveness of two different amendments for Cr(VI) removal was tested. Results showed a clear dependence of Cr(VI) decay on the amendment used. Notably, yeast extract (200 mg L -1 ) provided the highest Cr(VI) removal, in comparison with polyhydroxybutirrate (180 mg L -1 ), whereas no removal was detected in the not amended control reactors. Bioinformatic analyses are ongoing in order to investigate changes in the bacterial community structure.