The current study presents the experimental results investigating combustion characteristics of sewage sludge fuels (SS) reference to coal and wood pellet as the two typical base fuels. Two types of SS were produced by drying and hydrothermal carbonization technology. The composition analysis and the thermogravimetric analysis (TGA) showed that SS were highly volatile with low ignition temperature than coal and wood pellet. In the lab-scale bubbling fluidized bed experiments, the combustion gas composition and bed temperature were measured for the cases of single fuel and blended fuel. The morphology and the composition of fly ash collected at the cyclone were analyzed using particle size analyzer, ICP-OES, and SEM-EDS. In the single fuel cases, NOx and SO2 emission of SS were several times higher than the base fuels, but those could be reduced in the blend fuel cases while maintaining overall thermal input and bed temperature. The different size distribution and overall composition of fly ash for the single fuel cases became similar in the blend fuel cases. The change in the characteristics of fly ash was considered to be related to the distribution of mineral matters, such as Ca, K, and P in particular. (C) 2019 Elsevier Ltd. All rights reserved.