Maleke Maleke, Williams Peter, Castillo Julio, Botes Elsabe, Ojo Abidemi, DeFlaun Mary, van Heerden Esta
TIA/UFS Metagenomics Platform, Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, PO Box 339, Bloemfontein, 9300, South Africa.
Environ Sci Pollut Res Int. 2015 Jun;22(11):8442-50. doi: 10.1007/s11356-014-3980-7. Epub 2014 Dec 30.
High concentrations of uranium(VI) in the Witwatersrand Basin, South Africa from mining leachate is a serious environmental concern. Treatment systems are often ineffective. Therefore, optimization of a bioremediation system that facilitates the bioreduction of U(VI) based on biostimulation of indigenous bacterial communities can be a viable alternative. Tolerance of the indigenous bacteria to high concentrations of U and the amount of citric acid required for U removal was optimized. Two bioreactor studies which showed effective U(VI) removal more than 99 % from low (0.0037 mg L(-1)) and high (10 mg L(-1)) concentrations of U to below the limit allowed by South African National Standards for drinking water (0.0015 mg L(-1)). The second bioreactor was able to successfully adapt even with increasing levels of U(VI) feed water up to 10 mg L(-1), provided that enough electron donor was available. Molecular biology analyses identified Desulfovibrio sp. and Geobacter sp. among known species, which are known to reduce U(VI). The mineralogical analysis determined that part of the uranium precipitated intracellularly, which meant that the remaining U(VI) was precipitated as U(IV) oxides and TEM-EDS also confirmed this analysis. This was predicted with the geochemical model from the chemical data, which demonstrated that the treated drainage was supersaturated with respect to uraninite > U4O9 > U3O8 > UO2(am). Therefore, the tolerance of the indigenous bacterial community could be optimized to remediate up to 10 mg L(-1), and the system can thus be upscaled and employed for remediation of U(VI) impacted sites.
南非威特沃特斯兰德盆地采矿渗滤液中高浓度的铀（VI）是一个严重的环境问题。处理系统往往效果不佳。因此，基于对本地细菌群落的生物刺激来优化促进铀（VI）生物还原的生物修复系统可能是一种可行的替代方案。优化了本地细菌对高浓度铀的耐受性以及去除铀所需的柠檬酸量。两项生物反应器研究表明，从低浓度（0.0037 mg L⁻¹）和高浓度（10 mg L⁻¹）的铀中去除铀（VI）的效率超过99%，使其降至南非饮用水国家标准允许的限值（0.0015 mg L⁻¹）以下。第二个生物反应器即使在进水铀（VI）水平增加到10 mg L⁻¹时也能够成功适应，前提是有足够的电子供体。分子生物学分析在已知物种中鉴定出脱硫弧菌属和地杆菌属，它们已知能够还原铀（VI）。矿物学分析确定部分铀在细胞内沉淀，这意味着剩余的铀（VI）以铀（IV）氧化物的形式沉淀，透射电子显微镜-能谱分析（TEM-EDS）也证实了这一分析。这与根据化学数据建立的地球化学模型预测的结果一致，该模型表明处理后的排水相对于晶质铀矿> U₄O₉> U₃O₈> UO₂（非晶质）是过饱和的。因此，可以优化本地细菌群落的耐受性以修复高达10 mg L⁻¹的铀，该系统因此可以扩大规模并用于修复受铀（VI）影响的场地。
