Biological iron oxidation by Thiobacillus ferrooxidans and Leptospirillum ferrooxidans in a biofilm airlift reactor

In this study, the oxidation of ferrous iron by a mixed culture of Thiobacillus ferrooxidans and Leptospirillum ferrooxidans bacteria was investigated in a continuous biofilm airlift reactor. Small basalt particles (0.2 mm) were used as carrier material for biofilm formation. The reactor was operated at a constant temperature of 30degreesC and at pH values ranging from 1.3 to 1.7. The reactor was fed with a nutrient solution containing 5.6 g l(-1) ferrous iron, at various loading rates. Feasibility and engineering aspect of biological ferrous oxidation in an airlift reactor were investigated. Specific attention was paid to biofilm formation and competition between both types of bacteria. It was found that both types of acidophilic bacteria were capable of effective colonization of the carrier material, resulting in ferrous iron removal capacities of more than 0.05 mol l(-1) hr(-1). Coexistence of T. ferrooxidans and L. ferrooxidans in the system was observed by fluorescent in situ hybridization (FISH) measurement.