Influence of bicarbonate on the abundance of microbial communities capable of reducing U(VI) in groundwater

In order to investigate the influence of different concentrations of bicarbonate on the abundance of microbial communities capable of reducing U-(VI) in groundwater, 7 groups of experiments incubated with lactate and amended with 7 initial concentrations of bicarbonate (0, 5, 10, 15, 20, 25, and 30 mM), respectively, were conducted. It was found that U-(VI) concentration failed to decrease below the Chinese uranium wastewater discharge standard (0.05 mg L-1) when the initial bicarbonate concentration was higher than 10 mM. During the nitrate reduction, the abundance of nitrate reduction bacteria (NRB) was 22% in B0, while the abundance of NRB was 3.4% in B10 and B15. The main functional microbial community in B0 was NRB Brevundimonas, whose abundance was over 19%. During the U-(VI), sulfate, and Fe-(III) reduction, the abundance of sulfate and Fe reduction bacteria (SRB and FRB) was 44% in B0, while the abundance of SRB and FRB were 26% and 27% in B10 and B15, respectively. The main functional microbial communities capable of reducing U-(VI) in B0 were Cellulomonas, Desulfosporosinus, and Desulfovibrio, whose abundance was as high as 36%. The main microbial community capable of reducing U-(VI) in B10 was Desulfitobacterium, and its abundance was higher than 14%. The main functional microbial communities capable of reducing U-(VI) in B15 were Desulfovibrio and Geobacter, and their abundance was over 13%. The overall experimental results indicate that the higher initial bicarbonate concentration leads to the lower abundance of microbial communities capable of reducing U-(VI) in groundwater.