Electrical stimulation promotes synchronous nitrobenzene bio-degradation and vanadate bio-reduction

The combined pollution of nitrobenzene (NB) and pentavalent vanadium [V(V)] in groundwater brings great risks to the ecological environment and human health. In this study, we investigated the biological removal of NB and V(V) from the groundwater with electrical stimulation. Up to 94.3 +/- 1.32% of NB and 87.2 +/- 0.856% of V (V) were removed at 0.6 V. Although the removal of NB and V(V) was reduced at increased loading of NB or V (V), supplementing more ethanol substantially improved the removal performance. A few genera (e.g., Alkalibacter, Anaerovorax, Dechloromonas, Xanthobacter, Acetobacterium, and Clostridium_sensu_stricto_12) were distinctively enriched in the bioreactors spiked with both NB and V(V). The metagenome analysis revealed functional genes (e.g., nbzAa, catA, CYC, pilA) that were affiliated with NB and V(V) removal. It is speculated that the NB was first electrochemically reduced to aniline, and then mineralized to other intermediates (e.g., catechol). Cathode donating electron, glutathione and nitrite-reductase contributed to the bioreduction of V(V) to tetravalent vanadium. This study can advance our understanding of management of combined pollution of heavy metals and refractory organics in the groundwater.