In this paper, the leaching, toxicity behaviour and the radioactivity content of solid residues coming from the co-combustion of biomass with coal were studied. A variety of samples collected from semi-industrial scale tests were analysed for their leaching and toxicity properties. Natural radioactivity and radon exhalation rate were also measured in samples collected from tests performed in a pilot facility in Germany (IVD, University of Stuttgart) and large-scale power plants. The high toxicity levels detected in the ash samples of olive kernel could be attributed to the relatively increased concentrations of Zn, Ni, Mn, Co, Cd. The effect of biomass co-combustion on the radioactivity content of .y ash was dependent on the fuel mixture used as well as the ash sampling location along the flue gas pathway. Activity concentrations of most nuclides of interest, namely 238U, 226Ra, 210Pb and 232Th are comparable to those of .y ash produced when burning pure coal, while increased concentrations where observed for 40K. In some cases the artificial radionuclide 137Cs was also detected.

Keywords: : Co-combustion residues, TCLP method, Radioactivity