Concurrent reductive decontamination of chromium (VI) and uranium (VI) in groundwater by Fe(0)-based autotrophic bioprocess

The co-presence of chromium (VI) [Cr(VI)] and uranium (VI) [U(VI)] is widely found in groundwater, imposing severe risks on human health. Although zerovalent iron [Fe(0)] supports superb performance for bioreduction of Cr(VI) and U(VI) individually, the biogeochemical process involving their concurrent removal with Fe(0) as electron donor remains unexplored. In the 6-d batch study, 86.1% +/- 0.7% of Cr(VI) was preferentially eliminated, while 78.4% +/- 0.5% of U(VI) removal was achieved simultaneously. Efficient removal of Cr(VI) (100%) and U(VI) (51.2% similar to 100%) was also obtained in a continuous 160-d column experiment. As a result, Cr(VI) and U(VI) were reduced to less mobile Cr(III) and insoluble U(IV), respectively. 16 S rRNA sequencing was performed to investigate the dynamics of microbial community. Delftia, Acinetobacter, Pseudomonas and Desulfomicrobium were the major contributors mediating the bioreduction process. The initial Cr(VI) and hydraulic retention time (HRT) incurred pronounced effects on community diversity, which in turn altered the reactor's performance. The enrichment of Cr(VI) resistance (chrA), U(VI) reduction (dsrA) and Fe(II) oxidation (mtrA) genes were observed by reverse transcription qPCR. Cytochrome c, glutathione and NADH as well as VFAs and gas metabolites also

Automated summary

The coexistence of chromium (VI) and uranium (VI) in groundwater poses severe risks to human health. This study explores the concurrent removal of Cr(VI) and U(VI) using zerovalent iron (Fe(0)) as an electron donor. The results show that Fe(0) can effectively remove both Cr(VI) and U(VI), reducing them to less mobile and insoluble forms. Microbial communities, including Delftia, Acinetobacter, Pseudomonas, and Desulfomicrobium, play a crucial role in mediating the bioreduction process. The study also observed the enrichment of genes related to Cr(VI) resistance, U(VI) reduction, and Fe(II) oxidation, indicating the involvement of specific microbial activities.