Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

Abstract

AbstractBACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H2S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H2S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system.RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L−1 h−1 in a culture initially containing 19.5 g L−1 Fe2+ in the batch system. A maximum Fe2+ oxidation rate of 6.7 g L−1 h−1 was achieved at the dilution rate of 2 h−1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C.CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L−1 h−1 and 7 g L−1 h−1 for 3.5 g L−1 and 6 g L−1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L−1 and 21.3 g L−1, bio‐oxidation rate were 0.9 g L−1 h−1 and 0.55 g L−1 h−1, respectively. Copyright © 2008 Society of Chemical Industry