Abstract
The feasibility to dispose wastewater sewage sludge through thermal degradation methods, was studied in consideration of the recent European environmental directives, which limited the use of this solid waste as fertilizer. In particular, the pyrolysis of sewage sludge was investigated, in order to obtain a gas phase, rich in hydrocarbons, for a fuel gas use. The characterization of this produced gas phase, and the determination of its heat of combustion, are fundamental data for the application of a pyrolysis disposal method. For this reason, thermogravimetric coupled mass spectrometric and thermogravimetric coupled gas chromatographic and mass spectrometric analyses were carried out for the obtainment of an accurate characterization of the sewage sludge pyrolysis process. Tests on a laboratory-scale reactor were furthermore carried out with charges of 0.3 kg of sewage sludge. Analogously to the ashes of an incinerator plant, the pyrolysis solid residue is a waste with high content of hazardous heavy metal ions, and in consequence it must be stabilized. For this aim, vitrification is considered the best method which bears the immobilization of the heavy metal ions into a vitreous matrix. This vitrified material doesn't need landfill collocation, but it can be used as inert additive in ceramics and concretes field. On the basis of these considerations, the disposal of wastewater sewage sludge, through a pyrolysis-vitrification process, was studied, considering this two steps process as an integration of the depuration systems present in the wastewater treatment plant. In order to apply this disposal treatment for sewage sludge produced by the wastewater treatment plant, the resolution of the mass and energy balances was carried out by applying a thermochemical equilibrium model.