Evolution of Heavy Metals Leachability and Speciation in Residues of Sewage Sludge Treated by Microwave assisted Pyrolysis

摘要

In this study the sewage sludge are treated by microwave assisted pyrolysis (MAP) with different microwave receptors, and then, the immobilization of heavy metals in the residues are evaluated through the toxicity characteristic leaching procedure (TCLP) and sequential extraction procedure. The volatilization of Cd, Pb and Zn could be decreased by MAPs more efficiently than the conventional pyrolysis (CP). The average leaching percentages of Cu, Zn and Pb in residues produced by MAPs are decreased 90%, 88% and 81% more than the CP process respectively, and no leaching Cd is detected. Moreover, more than 67% of Cu, Pb, Zn and 55% of Cd in residues of MAP speciated into stable phase, which is higher than the metals in the residues of CP. The effect of heavy metals stabilized in residues of MAP was determined in the order as Cd > Cu > Pb > Zn. The results suggest the immobilization of heavy metals in the residues are enhanced in the process of MAP. This novel approach should be of significance in immobilizing heavy metals in residues of sewage sludge.