Pyrolysis Analysis and Solid Residue Stabilization of Polymers,Waste Tyres, Spruce Sawdust and Sewage Sludge

Purpose The pyrolysis thermal treatment of several waste such as polymers (PE, PVC, PS), sewage sludge, tyres, waste wood as spruce sawdust and the successive stabilization of the pyrolysis residue has been investigated on analytical and energetic point of view. This thermal process has been considered as it allows the reduction of the waste mass with the recovery of its energy content, through the exploitation of the produced gas phase as fuel. Methods Analyzed plastics are pure polymers: Polyethylene ‘‘Riblene FF22’’ and polystyrene ‘‘Edistir 1910’’ furnished by Enichem, while polyvinylchloride has been a K57 PVC furnished by EVC. The sewage sludge sample derives from the urban wastewater treatment plant of Trento, while the waste tyre is a SMR 10 Marangoni tyre. Spruce sawdust has been furnished by a neighbouring sawmill. The pyrolysis of the above indicated solid waste was studied by thermogravimetry coupled to mass spectrometry, TG-MS and TG-GC–MS. This analytical approach was followed by pyrplysis tests, carried out on a selection of the waste materials, by using a pyrolysis bench scale reactor. Result The pyrolysis of all the wastes takes place in the range of 400–600C and leads the reduction of the 90% of the mass for plastics, 50% for sludge, and ca. 60% for tyres, with production of a fuel gas phase particularly rich in hydrocarbons, with a estimated LHV from 15 to 32.8 MJ/kg for sewage sludge and plastics, respectively. A schematic energetic analysis is proposed implementing the pyrolysis stage with a vitrification process in order to obtain, in particular for sewage sludge residue, a product environmental friendly to use as raw material in industry. Conclusions The promising perspective of a two steps pyrolysis–vitrification process has been investigated to exploit the heating power of the resulting gas phase and to solve the environmental impact of heavy metals. The proposed analytical and energetic analysis looks promising for future improvements of this type of processes.