Kinetics of the Ferrous Iron Oxidation by Resuspended Cells of Thiobacillus ferrooxidans

Ferrous sulfate solutions with concentrations of up to the limit of solubility (70 g/L Fe 2+ ) were oxidized by free suspended cells of Thiobacillus ferrooxidans. The bacteria used were obtained from biofilm by resuspension. The oxidation rates were up to 2.2 g of ferrous iron per liter volume of liquid media per hour, which is more than 5 times higher than the maximal oxidation rates [0.4 g/(L·h)] reported in the literature. Kinetics of the process were studied in chemostat. A simple kinetic model based on the Monod equation assuming a competitive product inhibition and substrate inhibition mechanisms was used. The model described well the experimental data with input ferrous iron concentrations between 2 and 70 g of Fe 2+ /L. It was determined that temperatures between 18 and 37°C have almost no effect on the oxidation rate. The same effect was observed earlier for the oxidation of ferrous iron by biofilm of the same microorganisms. A suggestion is made that these bacteria change their activity owing to alterations during fixation in a biofilm. This change is irreversible.