Combustion of three different sewage sludge samples (B, F and S), one bituminous coal and sludge-coal blends were studied by TG dynamic runs carried out at 10 degreesC/min in the temperature range 25-800 degreesC. The sludge is mainly formed by two organic fractions with different reactivity; the less reactive fraction decomposes and bums at temperatures closer to those of coal, although, in general, slightly lower. For coal-sludge blends, no interactions between the components were detected. The Arrhenius kinetic parameters were calculated from the experimental results, considering the process as a series of consecutive first order reactions. Coal reactivity is scarcely modified as a consequence of a low addition of sludge (10 wt% blends). The 50 wt% blends show two different regions of reactivity. In the lower temperature region (about T < 350 degreesC), the blend reactivity is similar to that of sludge, while in the higher temperature region (T > 350 degreesC), it is similar to that of coal. (C) 2003 Elsevier Ltd. All rights reserved.