Catalytic pyrolysis: New approach for destruction of POPs in MWIs fly ash

Combined water washing with catalysis was applied in pyrolysis process to enhance the destruction efficiencies of PCDD/Fs and dl-PCBs in MWI fly ash. The results indicate that water or carbonated water washing effectively reduces chloride content in fly ash but it contributes minor enhancement of PCDD/Fs and dl-PCBs destructions achieved with pyrolysis process. Being pyrolyzed at temperature of 350 degrees C for 1 h, the removal efficiencies of 96.7%, 98.5% and 96.2% for PCDD/Fs, and 79.3%, 92.3% and 87.3% for dl-PCBs are achieved for unwashed fly ash, water washed fly ash and carbonated water washed fly ash, respectively. Nonetheless, TEQ concentrations of PCDD/Fs and dl-PCBs in pyrolyzed fly ash remain higher than the European end-of-waste criteria (20 pg WHO-TEQ/g). As palladium was added to the system as catalyst, the decay rates of PCDDs, PCDFs and dl-PCBS in fly ash increase significantly even with a much shorter pyrolysis time (15 min). Increases of PCDD/Fs and dlPCBs destruction efficiencies by pyrolysis combined with catalysis could be ascribed to the inhibition of pre cursor formation at 200-300 degrees C by Pd. Synergistic effect of water washing and catalysis in pyrolysis process at 350 degrees C reduces the concentrations PCDD/Fs and dl-PCBs to lower than 20 pg WHO-TEQ/g, enabling the reuse of MSW fly ash.

Automated summary

This study investigated the combination of water washing and catalysis in the pyrolysis process, finding that at 350 degrees Celsius, this method can reduce the concentrations of PCDD/Fs and dl-PCBs, enabling the reuse of MSW fly ash.