Kinetics of Iron Oxidation byLeptospirillum ferriphilum Dominated Culture at pH Below One

The kinetics of ferrous iron oxidation by Leptospirillum ferriphilum (L. ferriphilum) dominated culture was studied in the concentration range of 0.1–20 g Fe2þ/L and the effect of ferric iron (0–60 g Fe3þ/L) on Fe2þ oxidation was investigated at pH below one. Denaturing gradient gel electrophoresis of PCR amplified 16S rRNA genes followed by partial sequencing confirmed that the bacterial community was dominated by L. ferriphilum. In batch assays, Fe2þ oxidation started without lag phase and the oxidation was completed within 1 to 60 h depending on the initial Fe2þ concentration. The specific Fe2þ oxidation rates increased up to around 4 g/L and started to decrease at above 4 g/L, indicating substrate inhibition at higher concentrations. The Haldane equation fitted the experimental data reasonably well (R2 = 0.90), with maximum specific oxidation rate (qm) at 2.4 mg/mg VS/C1 h. Competitive inhibition by Fe3þ was observed, with the competitive inhibition constant (Kii) being 830 mg/L. The threshold Fe2þ concentration increased linearly with rising Fe2þ and Fe3þ concentrations. These findings support the potential use of L. ferriphilum-dominated cultures for biologically regenerating concentrated Fe3þ sulfate solutions in various applications.