A field study of polychlorinated dibenzo-p-dioxins and dibenzofurans formation mechanism in a hazardous waste incinerator: Emission reduction strategies

To clarify the dominant formation mechanism of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and reduce PCDD/F emissions in full-scale hazardous waste incinerators (HWIs), three tests were designed by adding different PCDD/F precursors in phenol-containing raw material. Flue gas from three stages of the incineration facility, as well as bottom ash and fly ash were collected to investigate formation pathways, emission characteristics and mass balance of PCDD/Fs. The results showed that in tests A and C, the PCDD/F emission levels were 0.02 and 0.83 ng I-TEQ Nm⁻³, with adding naphthalene and p-dichlorobenzene, respectively. Test B, the control group, only incinerated raw materials, resulting in 0.72 ng I-TEQ Nm⁻³ PCDD/F emissions. PCDD/F formation mechanism analysis suggested that high-temperature radical-molecule reaction was the dominate pathway in test A, while for test B, memory effect in the air pollution control devices (APCDs) led to high PCDD/F emissions. With the addition of p-dichlorobenzene in test C, PCDD/F levels at the quenching tower outlet were one order of magnitude higher than those observed at the inlet, indicating that the quenching tower failed to suppress the formation of PCDD/Fs. The PCDD/PCDF ratios indicate that with the abundance of PCDD/F precursors, surface-mediated precursor reaction is the dominant formation mechanism in low-temperature stages. These finding raise the following strategies for industry to control PCDD/F emissions: (1) strict regulation of the organochlorine content in feed material; (2) frequent and thorough cleaning the APCDs; (3) optimizing the injection rate of activated carbon.