Thermogravimetric (TC) analysis was used to study and compare the combustion of sewage sludge (SS), animal manure (AM) and the organic fraction of municipal solid waste (OFMSW). TG curves are in correspondence with the volatiles and carbon content of the materials studied. Non-isothermal thermogravimetric data were used to assess the kinetics of the combustion of these carbonaceous materials. The paper reports on the application of a model-free isoconversional method for the evaluation of the activation energy corresponding to the combustion of these biowastes. The activation energy related to AM combustion (E similar to 140 kJ mol(-1)) was similar to that corresponding to SS (E similar to 143 kJ mol(-1)) while the OFMSW showed to have a higher value (E similar to 173 kJ mol(-1)). (C) 2008 Elsevier Ltd. All rights reserved.