An autotropic Thiobacillus sp. CH11 was isolated from piggery wastewater containing hydrogen sulphide. The removal characteristics of hydrogen sulphide by Thiobacillus sp. CH11 were examined in the continuous system. The hydrogen sulphide removal capacity was elevated by the BDST (Bed Depth Service Time) method (physical adsorption) and an immobilized cell biofilter (biological conversion). The optimum pH to remove hydrogen sulphide ranged from 6 to 8. The average specific uptake rate of hydrogen sulphide was as 1.02 x 10(-13) mol-S cell(-1) h(-1) in continuous systems. The maximum removal rate and saturation constant for hydrogen sulphide were calculated to be V-m = 30.1 mmol-S day(-1) (kg-dry bead)(-1) and K-s = 1.28 mu mol dm(-3), respectively. A criterion to design a scale-up biofilter was also studied. The maximum inlet loading in the linear region (95% removal) was 47 mmol-S day(-1) (kg-dry bead)(-1). Additionally, the biofilter exhibited high efficiency (>98.5%) in the removal of hydrogen sulphide at both low (<0.026 mg dm(-3)) and high (0.078 mg dm(-3)) concentrations. The results suggested that the Thiobacillus sp. CH11 immobilized with Ca-alginate is a potential method for the removal of hydrogen sulphide.