Thiobacillus ferrooxidans could be used to regenerate ferrous sulphate solution produced in a process to remove H2S from waste gas if the reaction rate could be increased. The aim of the present study was to increase the volumetric productivity by using immobilized cells. Kinetic data of ferrous iron oxidation were determined in fixed-bed and fluidized-bed reactor configurations with different support materials in order to find the most practical system for scale-up. By using a fixed-bed reactor the iron oxidation rate can be increased to 3.6 g l(-1) h(-1), fivefold higher than suspended cells, and results in a bioreactor of reasonable size. With the kinetic data obtained, the biological reaction is no longer a limiting factor for industrial-scale application.