Biostimulation of Indigenous Microbes for Uranium Bioremediation in Former U Mine Water: Multidisciplinary approach assessment

Characterizing the physicochemistry and microbial diversity of U mine water is a key prerequisite for understanding the biogeochemical processes occurring in these water mass and for the design of an efficient bioremediation strategy. This study has collected and analysed in reference date measurements water samples from two former U-mines (Schlema-Alberoda and Pöhla, Wismut GmbH) in East Germany. The samples from both mines are pH-circumneutral (7.3 and 6.6) and show reducing conditions (E_H: +139 and –91 mV). Interestingly, the U and sulphate concentrations of Schlema-Alberoda mine water (U: 1 mg/L; SO₄ ²⁻: 335 mg/L) are 2 and 3 order of magnitude higher than those of the Pöhla samples (U: 0.01 mg/L; SO₄ ²⁻: 0.5 mg/L), respectively. U, SO₄ ²⁻ and Fe seem to shape the differential microbial diversity of the water from both mines. Microbial diversity analysis revealed the distribution of bacteria with U(VI)-reducing capacity and the ability to maintain the stability of reduced U-species (e.g., Desulfurivibrio, Gallionella and Sulfuricurvum). In addition, water from the mines harbour wood-degrading fungal communities (e.g., composed of Cadophora and Acremonium) providing potential electron donors which promote the growth of U-reducing bacteria. For the design of a bioremediation strategy, we conducted a preliminary U-bioreduction experiment to screen for suitable electron donors (glycerol, vanillic acid and gluconic acid). We also observed that high levels of soluble U (initially present as Ca₂UO₂(CO₃)₃(aq) and UO₂(CO_{3) 3} ⁴⁻), Fe and SO₄ ²⁻ were removed by 98, 95 and 53%, respectively from the mine water by using glycerol as electron donor. The remaining U concentrations after bioreduction meet regulatory standards for beneficial reuse of U mine water. As a whole, the results reveal the chemical factors influencing the microbial community in U mine water and may contribute to the design of bioremediation strategies based on the biostimulation of U-reducing bacteria for low U concentrations in contaminated water.