The gasification of dried sewage sludge was performed using various additives (activated carbon, Ni-impregnated activated carbon, dolomite, and CaO) in a two-stage gasifier to produce a tar-free gas with a low NH3 content. This research also examined the effect of feed rate on the tar removal efficiency and the stability of the two-stage gasification system conducting a similar to 3.7 h gasification. In all experiments, natural olivine was used as a fluidized bed material, and air as a gasifying agent. The equivalence ratio was kept almost constant at similar to 0.36. When Ni (8.9 wt%)/activated carbon was applied, a tar-free gas with 31.3 vol% H-2 and 114 ppm NH3 was obtained, with a tar removal efficiency of 97%. A higher feed rate turned out to have a negative effect on the tar removal. The gasification performed using multiple additives for similar to 3.7 h produced a tar-free gas with 146 ppm NH3. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.