Enzymatically‐mediated uranium accumulation and uranium recovery using a Citrobacter sp. Immobilised as a biofilm within a plug‐flow reactor

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Biofilm‐immobilised Citrobacter sp. removed uranyl ion from flows supplemented with glycerol 2‐phosphate. The metal uptake mechanism was mediated by the activity of a cell‐surface bound phosphatase that precipitated liberated inorganic phosphate with uranyl ion as HUO 2 PO 4 ·4H 2 O at the bacterial surface. A modified integrated form of the Michaelis–Menten equation is proposed to describe the removal of metal ion by a columnar bioreactor, where the efficiency of metal removal is semi‐quantitatively related to the input flow rate, the total enzyme loading ( E 0 ) and the bioreactor activity. With biofilm‐immobilised bacteria, E 0 was further divisible (split) into subparameters of phosphatase titre per bacterium and total biomass surface area. Varying the split E 0 and the reaction temperature modified the bioreactor performance. The immobilised bacteria retained high metal loads without loss in steady‐state activity. Accumulated metal was recovered as a concentrated solution.