A biofiltration system with sulfur oxidizing bacteria immobilized on granular activated carbon (GAC) as packing materials had a good potential when used to eliminate H2S. The sulfur oxidizing bacteria were stimulated from concentrated latex wastewater with sulfur supplement under aerobic condition. Afterward, it was immobilized on GAC to test the performance of cell-immobilized GAC biofilter. In this study, the effect of inlet H2S concentration, H2S gas flow rate, air gas flow rate and long-term operation on the H2S removal efficiency was investigated. In addition, the comparative performance of sulfide oxidizing bacterium immobilized on GAC (biofilter A) and GAC without cell immobilization (biofilter 13) systems was studied. It was found that the efficiency of the H2S removal was more than 98% even at high concentrations (200-4000 ppm) and the maximum elimination capacity was about 125 g H2S/m(3) of GAC/h in the biofilter A. However, the H2S flow rate of 15-35 l/h into both biofilters had little influence on the efficiency of H2S removal. Moreover, an air flow rate of 5.86 l/h gave complete removal of H2S (100%) in biofilter A. During the long-term operation, the complete H2S removal was achieved after 3-days operation in biofilter A and remained stable up to 60-days. (c) 2008 Elsevier Ltd. All rights reserved.