Pelletizing and combustion behaviors of wood waste with and without additive addition were investigated in this study. It was found that the wood waste pellets have a high potential for slag formation during combustion and can cause operational problems. With additives addition, no significant changes were observed regarding mechanical properties of the wood waste pellets. Sewage sludge addition was found to have positive effects on NOx and CO emissions during combustion. Both sewage sludge and marble sludge addition have evident influence on slag formation during combustion. Sewage sludge addition reduced the formed slag amount and sizes, and therefore improved the boiler operation. Marble sludge eliminated the slag formation during the wood waste pellets combustion.