Influence of enriched nitrate reducing bacteria communities on bacterial community structure and groundwater condition during in situ bioremediation of nitrate in acidic uranium-contaminated groundwater.

In-situ leaching (ISL) is the predominant technology used in uranium mining currently, although it leads to significant environmental challenges. Nitrates, a key component in leaching agents, not only pose a threat to human health but also impede the bioreduction of U(VI) in uranium-contaminated water. In this study, the nitrate reducing bacterial (NRB) communities adapted to acidic uranium-contaminated groundwater from a site in Northwest China were gained by an enrichment micro-model. The effects of the NRB communities on the groundwater parameters and microbial diversity were evaluated using the groundwater-core column leaching system during the in-situ bioremediation of nitrate. The enrichment experiments revealed that NRB communities adapted to acidic uranium-contaminated groundwater were successfully enriched, of which Tumebacillus was the main functional bacterium. The column leaching experiment results showed that adding NRB communities successfully reduced nitrate levels from 100.91 mg/L to 0.7 mg/L in just 8 days, improved groundwater acidity and redox conditions. Additionally, the metagenomic analysis showed that introducing NRB communities increased biomass and indigenous NRB, but decreased microbial diversity. The KEGG enrichment analysis suggested that butanoate metabolism and valine, leucine and isoleucine degradation were promoted by adding enriched NRB communities. This research lays the groundwork for nitrate removal from contaminated groundwater in areas affected by ISL in uranium mines, setting the stage for future in situ bioremediation of U(VI).