The removal of hydrogen sulfide (H2S) was investigated in a lab scale biofilter packed with biomedia, encapsulated by sodium alginate and polyvinyl alcohol (PVA). The main H2S oxidation products were SO42-, SO32-, S2- and S-0. The immobilized cell biofilter required no separate acclimatization period and showed high removal efficiencies (RE) within the first few days of experiments. The removal efficiencies in the biofilter were consistently greater than 99% even when H2S loading was 6 g m(-3) h(-1). The maximum elimination capacity achieved in this study is 8 g H2S m(-3) h(-1) at a loading rate of 13 g H2S m(-3) h(-1). The response of the immobilized cells to fluctuations in inlet concentration and flow rate was determined by subjecting the biofilter to inlet loads of up to 10 g HZS m(-3) h(-1). The biofilter responded effectively to these shock loading conditions and convalesced rapidly within 4-8 h. Pressure drop values were consistently less throughout the operational period. The results from this study suggest that an immobilized cell biofilter is effective in treating H2S under steady and transient operating conditions. (c) 2007 Elsevier Ltd. All rights reserved.