Abstract
The ex-situ bioremoval of U(VI) from contaminated water using Acidithiobacillus ferrooxidans strain 8455 and 13538 was studied under a range of pH and uranium concentrations. The effect of pH on the growth of bacteria was evaluated across the range 1.5 – 4.5 pH units. The respiration rate of At. ferrooxidans at different U(VI) concentrations was quantified as a measure of the rate of metabolic activity over time using an oxygen electrode. The biosorption process was quantified using a uranyl nitrate solution, U-spiked growth media and U-contaminated mine water. The results showed that both strains of At. ferrooxidans are able to remove U(VI) from solution at pH 2.5 – 4.5, exhibiting a buffering capacity at pH 3.5. The respiration rate of the micro-organism was affected at U(VI) concentration of 30 mg L-1. The kinetics of the sorption fitted a pseudo-first order equation, and depended on the concentration of U(VI). The KD obtained from the biosorption experiments indicated that strain 8455 is more efficient for the removal of U(VI). A bioreactor designed to treat a solution of 100 mg U(VI) L-1 removed at least 50% of the U(VI) in water. The study demonstrated that At. ferrooxidans can be used for the ex-situ bioremediation of U(VI) contaminated mine water.
Highlights
An increase in anthropogenic activity through uranium mining and milling for the nuclear fuel cycle, and other industrial processes, has resulted in elevated levels of uranium within the environment
The effect of pH on the growth of At. ferrooxidans was quantified at different initial growth medium pH-values
Studies conducted with solution pH in the range 1.5–4.5 show that At. ferrooxidans growth is best at pH 3.5 and hindered at pH 1.5
Summary
An increase in anthropogenic activity through uranium mining and milling for the nuclear fuel cycle, and other industrial processes, has resulted in elevated levels of uranium within the environment. Low levels of uranium are released during uranium mining and high levels are released during uranium enrichment and reprocessing (Lloyd and Renshaw, 2005). Leaching of these waste materials into nearby ground water and soil sediments, due to ineffective storage mechanisms, results in radionuclides entering the food and water supply, becoming a hazard to human health (Choy et al, 2006; Gavrilescu et al, 2009). Contamination by uranium from mining activities is extensive in surface and ground waters across the world, and the consequences of this are detrimental to the health of the natural environment, since they have an impact on human health. The contamination of groundwater from uranium mining activities is limiting the access to clean water
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