Insights into pyrolysis characteristics of Brazilian high-ash sewage sludges using thermogravimetric analysis and bench-scale experiments with GC-MS to evaluate their bioenergy potential

This paper is the first comprehensive report about the renewable fuels produced from the pyrolytic conversion of anaerobic and aerobic Brazilian high-ash sewage sludges. The study was divided into three steps: (1) an in-deep evaluation of physicochemical characteristics of both sewage sludges; (2) thermogravimetric analysis under inert conditions for determining bench-scale pyrolysis conditions; (3) characterization of volatile pyrolytic products from fixed bed reactor using GC/MS analysis. The anaerobic and aerobic sewage sludges present substantial high heating values and high contents of ash and sulfur, which are adverse properties for solid fuels. Regarding the pyrolytic behavior, the sewage sludge samples presented a two-step thermal decomposition process. The bio-oil produced from pyrolysis indicates that the high-ash sewage sludges are a source of high value-added chemicals, such as aliphatic and monoaromatic hydrocarbons. In addition, the pyrolysis can promote the production of a hydrogen-rich syngas for thermal boilers or engines use. In this research, it was demonstrated that the pyrolysis process of Brazilian high-ash sewage sludge can be applied for the production of useful biofuels - as bio-oil and bio-syngas - also adding value to this waste, thus contributing to the establishment of renewable source of bioenergy. •Upgrading of Brazilian high-ash sewage sludge (SS) via pyrolysis.•Bio-oil achieved can be a source of valuable chemicals.•The HHV values for SS are compared to low-rank coals.•The GC-MS analysis indicated high concentration of aliphatic compounds.•Pyrolysis is a green and clean route to useful biofuels from SS.