Pyrolysis of waste

The management of sewage sludge in an economically and environmentally acceptable manner is one of the critical issues facing society today. In fact, the amount of sludges produced by wastewater treatment plants is going to dramatically increase in both industrialized and emerging countries. Recycling to agriculture (landspreading), incineration or landfilling are the most common disposal routes. However, landspreading leads to an increase in concentration of heavy metals in the soils and indirect emissions into air and water. Disposal by landfilling requires a lot of space and poses a potential environmental hazard. On the other hand, although incineration can provide a large volume reduction and energy recovery, it generates emissions into the air, soil and water. Several technologies presenting an alternative to conventional combustion processes are currently being developed. These technologies mainly include the wet oxidation process, pyrolysis and the gasification process. Pyrolysis has significant advantages over the other methods. Pyrolysis produces more useful products; gas, oil and solid char which may be used as fuels or a feedstock for petrochemicals and other applications. In addition, heavy metals (expect mercury and cadmium) could be safely enclosed in the solid char. Pyrolysis of sewage sludge under different conditions has been studied to investigate the pyrolysis mechanism and to characterize the gases, oils and solid char. Due to the advantages of pyrolysis, in this study, pyrolysis of two different types of sludge was carried out in a fixed-bed
reactor. The main goal of this study was to characterize the composition of gas and liquid products obtained from pyrolysis to determine their utilization area. To understand the thermal behaviour of sludges during pyrolysis, thermogravimetric analysis was also performed. At present, one of the sludges used in this study is disposed of by incineration, the other is disposed off by landfilling