Batch kinetics of ferrous iron oxidation by Leptospirillum ferriphilum at moderate to high total iron concentration

A study of the kinetics of ferrous iron oxidation by a free suspended culture of the bacterium Leptospirillum ferriphilum in batch regime at moderate to high iron concentrations was conducted. A circulating bed airlift bioreactor was used in order to obtain reliable biokinetic data, unaffected by biofilm growth. The two major factors in consideration were the effects of the pH and the total iron concentration in the range of 5–40 g/L. The optimal pH was found between 1.05 and 1.80. In this range a strictly growth associated biooxidation with constant yield coefficient was proven, while at suboptimal pH values non-growth associated iron biooxidation was shown at pH as low as 0.4. This effect was taken into consideration for the derivation of a Monod-type kinetic model, derived on first principles from the electrochemical-enzymatic model for ferrous iron biooxidation. Our model shows a linear dependence between the apparent half-saturation constant (Kapp) and the total iron concentration in studied range of iron concentration.