This is the study of environmental implications of sewage sludge cogasification mixed with biomass wastes (straw pellets). NH 3, H 2S, and HCl contents of syngas were compared to those produced during cogasification of sewage sludge with coal. In the presence of straw pellets, lower concentrations of NH 3 and higher contents of HCl were obtained, probably due to its low and high contents of N and Cl, respectively. However, NH 3 and HCl contents in the syngas were very low and similar for both sewage sludge blends with straw pellets or with coal, because most of these compounds were retained in the condensation system of the gasification installation. Lower H 2S levels were also measured when blends of sewage sludge with straw pellets were used, probably due to the lower sulfur contents of straw pellets. The results obtained show that it is possible to cogasify sewage sludge with either biomass, such as straw pellets, or coal, without major modifications in previously existing gasification installations. H...