Pseudomonas stutzeri, a facultative anaerobe sourced from soil in a uranium mine in Limpopo, South
Africa, reduced uranium-6 (U(VI)) to uranium-4 (U(IV)) in batches under a relatively high initial U(VI)
concentration ranging from 30 to 400 mg/L (pH 5 to 6). U(VI) reduction was rapid during the first 4 to
6 h of incubation followed by slower reduction rates at incubation times longer than 6 hours.
Equilibrium conditions were only obtained after incubation for 24 h. The reduced U(VI) was recovered
in solution as a hydroxide which was determined to consist of U(IV).
A kinetic model based on enzyme kinetics produced the best fit of the optimised model to experimental
data of U(VI) versus time in batch cultures of Pseudomonas stutzeri. The parameters: maximum
specific uranium-6 reduction rate coefficient (ku), half velocity concentration (Ku), and uranium-6
reduction capacity of cells (Tc) were estimated using the data from the 200 mg/L batch. The
parameters obtained in the 200 mg/L batch were then used to simulate the concentration in the other
batches at lower and higher initial U(VI) concentrations. The reduction capacity Tc remained stable but
a loss of accuracy was observed with increasing initial U(VI) concentration.
Numerous batch experiments were conducted to establish kinetic parameters that will be used later for
scale-up purposes. The knowledge gained from such processes will be of practical value in predicting
effluent response to diverse loading conditions.