Transformation of mono- to octa- chlorinated dibenzo-p-dioxins and dibenzofurans in MWI fly ash during catalytic pyrolysis process

Total concentrations of mono- to octa-CDD/Fs in fly ash (FA) generated from municipal waste incinerator (MWI) are analyzed to study the transformation of total PCDD/Fs during thermal and catalytic pyrolysis processes. The clean-up procedure of mono- to octa-CDD/Fs in FA samples via activated carbon can be considered as cost-effective and relatively simple. In untreated FA, mono- to tri-CDD/Fs homologues account for 63.8% while tetra- to octa-CDD/Fs homologues account for 36.2% of total PCDD/Fs. After thermal pyrolysis, the contribution of mono- to tri-CDD/Fs homologues increases to 88.3% while that of tetra- to octa-CDD/Fs homologues reduces significantly to 11.7%. Four catalysts including Fe/C, Co/C, Ni/C and Cu/C are applied as catalyst individually in FA catalytic pyrolysis process and the results indicate that Ni/C is the most effective catalyst for PCDD/Fs destruction. In addition, the effects of catalyst size and the recyclability of catalyst are studied to further enhance the applicability of this technique for FA treatment. Finally, the reaction kinetics of thermal and catalytic pyrolysis processes are evaluated as an example to predict the required pyrolysis time to treat FA with different PCDD/F concentrations to meet the goal of ≤ 20 pg I-TEQ/g for reuse purposes.