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HIGHLIGHTS• Flammability parameters of sludge are presented.• Relationships between chemical and flammability properties of sludge are analyzed.• Physical and chemical properties of sludge dusts affects their explosibility.• Seasons and origins of sludge should lead to a differentiation among samples. ABSTRACTThe treatment and disposal of sewage sludge is becoming an urgent need whereby different technologies were developed and integrated into the waste cycle all over the world. One ofthe most used technologies is the thermal drying ofthe sludge. Thermally dried sewage sludge has interesting properties that allow its use as an alternative fue!, but also needs some consideration from the point of view of its safe operation.The aim ofthis study was the research on the flammability properties of sewage sludge, including ignition sensitivity, explosion severity, thermal sensitivity and thermal stability. Furthermore relationships among those properties and composition parameters have been determined, added to the study of their variation depending on their origin or season. Finally, properties related to spontaneous combustion were determined. To study these relationships and characteristics sludge samples were selected from different locations in Spain and taken during different seasons.

The use of renewable energy has increased in the last decades including the consumption of biofuels, so the research focused on improving these energetic vectors has increased too, developing techniques that enhance energetic properties of these fuels. In this context, torrefaction is a thermal pre-treatment that diminishes the main disadvantages present in biomass such as hygroscopicity, low calorific value per unit mass and high susceptibility to self-ignition. In this study raw and torrefied palm oil wastes samples are tested using thermogravimetric analysis (TGA) in order to study the influence of torrefaction on combustion kinetic parameters using Coats-Redfern and Freeman-Carroll methods, showing that torrefaction increases activation energy as it enhances thermal stability of the samples. The composition of the samples is also estimated using TGA through Fraser-Suzuki deconvolution showing the changes of lignin, cellulose, and hemicellulose due to torrefaction process.