Pyrolysis of sewage sludge samples from three Asturian urban wastewater treatment plants was carried out. One high volatile bituminous coal and its blends with 10 and 50 wt% of sludge were studied by thermogravimetry. The same operational conditions (a constant heating rate of 10 degreesC/min in the temperature range 25-800 degreesC and a N-2 flow of 200 cm(3)/min) were maintained throughout. The results indicate that sludge is formed by two organic fractions with different reactivity, whose devolatilisation processes partially overlap. Both fractions are more reactive than coal, since they decompose and devolatilise at temperatures lower than coal. Under oxidizing conditions, the action of oxygen during pyrolysis depends on the conditioning of sludge. If sludge is treated with FeCl3, oxidative pyrolysis takes place. The behaviour of sludge-coal blends is intermediate between those of the coal and the corresponding sludge, without interactions between both blend components. In addition, a kinetic analysis was performed to fit thermogravimetric data, the global processes being considered as a series of consecutive first order reactions. A reasonable fit to the experimental data was obtained for all materials and their blends. (C) 2004 Elsevier Ltd. All rights reserved.