Multi Mechanism Synergistic Treatment of Uranium-contaminating Water Body Mediated by Indigenous Bacteria

Abstract

The uranium-containing wastewater produced in the process of uranium mining and nuclear energy utilization poses a serious potential threat to the ecological environment and human health. It is an urgent environmental problem to be solved. Microbial remediation has the advantages of simple operation design, low cost, high feasibility, and little environmental interference. There are four mechanisms of interaction between microorganisms and U(Ⅵ): biosorption, biomineralization, bioreduction and bioaccumulation. In order to study the multiple remediation mechanism of uranium-contaminating water body mediated by indigenous bacteria, in this study, β-sodium glycerophosphate (GP) was used as the sole carbon and phosphorus source to induce the conversion of free U(Ⅵ) in solution to solid-phase precipitation under the degradation of indigenous phosphorus-dissolving bacteria. The objective is to investigate whether there are multiple mechanisms at play in the biomineralization of phosphate that occurs in the presence of added exogenous organophosphorus. The results of the solution parameters show that the removal of uranium reaches 90.68% at 36 h and 98.34% at 228 h. The stability analysis of the product shows that the desorption rate of uranium is 80.28% at 40 h and 30.23% at 228 h. The occurrence of biosorption, mineralization, reduction, and accumulation is verified by SEM-EDS, FT-IR, XRD, XPS, and TEM, respectively. At the early stage it is found that soluble U(Ⅵ) first attaches to the cell surface. It combines with hydroxyl, phosphate group and amide through electrostatic action and complexation to provide initial nucleation sites for the formation of U(Ⅵ) biominerals. Subsequently, XPS and XRD results jointly demonstrate that the solid uranium product is UO2 in the crystalline state. And U(Ⅵ)-phosphate mineral appeares in the form of Metaankoleite K(UO2)(PO4)·3H2O. The crystallinity of U(Ⅵ)-phosphate minerals becomes better with increasing reaction time. The appearance of fibrous and granular structural deposits around, on the surface and in the body of the bacteria is also found by TEM. Metaankoleite K(UO2)(PO4)·3H2O is also found inside the cells. The composition of this flora is unclassified_f_Enterobacteriaceae (53.15%), lysinibacillus (42.05%), dysgonomonas (2.79%), citrobacter (1.13%) and petrimonas (0.88%). Unclassified_f_Enterobacteriaceae plays a major role in the whole system. It has the functions of biosorption, biomineralization, bioreduction and bioaccumulation. The above results indicate that in complex and diverse outdoor environments, not only one type of microorganism is involved. It is more practical to study the remediation of uranium-containing wastewater by indigenous bacteria. Moreover, the indigenous bacteria may have the result of multiple mechanisms in the process of uranium remediation.

Keywords

• uranium
• microbial remediation
• indigenous bacteria
• biomineralization
• synergistic effect