Study of the Potential Ecological Risk of Heavy Metals in the Residue from Thermal Conversion of a Sewage Sludge

Abstract

The thermal conversion of the sewage sludge by pyrolysis, gasification and combustion can be an attractive alternative because it reduces the volume of the residue and improve its properties for safe disposal. However, the high content of some heavy metals in sewage sludge has to be carefully considered to come up with rational and sustainable disposal methods. Therefore, the study of the heavy metals distribution in the final residue after the thermal conversion of the sewage sludge is a key topic in order to implement clean methods to valorize sewage sludge. Tests were performed in a horizontal fixed-bed reactor using both nitrogen (pyrolysis) and air (combustion) atmospheres at different temperatures for tests of 20 min duration. At the end of each test, the final residue was collected, and the concentration of main heavy metals was measured by ICP. The results were analyzed through various indexes to establish the enrichment of the species in different ash stream and to assess the potential ecological risk of heavy metals. Finally, obtained value were compared with existing works and standards to assess potential the application of proper management methods.