Effect of bioleaching on hydrogen-rich gas production by steam gasification of sewage sludge was carried out in a lab-scale fixed-bed reactor. The influence of sewage sludge solids concentrations (6-14% (w/v) in 2% increments) during the bioleaching process and reactor temperature (600-900 degrees C in 100 degrees C increments) on gasification product yields and gas composition were studied. Characterization of samples showed that bioleaching treatment, especially in 6% (w/v) sludge solids concentration, led to metal removal effectively and modifications in the physicochemical property of sewage sludge which was favored for gasification. The maximum gas yield (49.4%) and hydrogen content (46.4%) were obtained at 6% (w/v) sludge solids concentration and reactor temperature of 900 degrees C. Sewage sludge after the bioleaching treatment may be a feasible feedstock for hydrogen-rich gas product. (C) 2015 Elsevier Ltd. All rights reserved.