In the present work, low grade activated carbon was upgraded by steam activation to improve its surface properties and further impregnated with potassium hydroxide (KOH) to promote the H2S chemisorption for desulfurization applications. The H2S adsorption performance of these prepared samples was tested at ambient temperature under various operating conditions i.e. in the presence of isolated and integrated relative humidity (70%), 02 (2%), and CO2 (40%). It was found that the KOH impregnated activated carbons provide significantly higher H2S adsorption capacity and breakthrough time than the non-impregnated sample. Importantly, the presence of 02 in the gas stream greatly increases the breakthrough time of H2S adsorption, while the presence of humidity significantly increases the H2S adsorption capacity; these positive effects are related to the promotion of H2S oxidation to elemental sulfur and H2S dissociation. In contrast, the presence of CO2 strongly inhibited H2S adsorption due to competitive adsorption and reaction between CO2 and H2S, particularly for the KOH impregnated samples. Nevertheless, it was revealed from the study that the presence of 02 and humidity along with CO2 can efficiently minimize this negative effect; therefore, this highlights the importance of 02 and humidity addition for biogas purification. (C) 2014 Elsevier B.V. All rights reserved.