It has been demonstrated that the bacterium Thiobacillus denittiicans may be readily cultured aerobically and anaerobically in batch and continuous cultures on hydrogen sulphide (H2S) gas under sulphide-limiting conditions. Under these conditions sulphide concentrations in the culture medium were less than 1 FM resulting in very low concentrations of H,S in the reactor outlet gas. The stoichiometries of both the aerobic and anaerobic reactions were determined and stable reactor operation demonstrated for up to five months. Maximum loading of the biomass was determined to be 5.4-7.6 mmoles H$Yh-g biomass under anaerobic conditions and 15.1-20.9 mmoles H$Yh-g biomass under aerobic conditions. Indicators of reactor upset were determined and recovery from upset demonstrated. Heterotrophic contamination was shown to have negligible effect on reactor performance with respect to hydrogen sulphide oxidation. In fact, growth of T: denitrificans in the presence of floe-forming heterotrophs produced a hydrogen sulphide active floe with excellent settling characteristics. A case study of the application of this technology to the removal and oxidation of HP!3 from biogas is presented.