Degradation of dioxins in chelated municipal solid waste incineration fly ash by low-temperature pyrolysis

In this study, low-temperature pyrolysis is applied to raw and chelated municipal solid waste incinerator fly ash to degrade and remove PCDD/F (polychlorinated dibenzo-p-dioxins, and dibenzofurans) and corresponding I-TEQs (international toxic equivalents), respectively. Additionally, PCDD/F degradation pathways are identified based on PCDD/F signatures. From the analysis of the average signal intensity of dioxin isomers in thermally treated fly ashes, the PCDD/F degradation rate was between 89.97 and 99.80 %, and the I-TEQs removal rate was 98.96 and 99.90% across all samples compared to untreated raw fly ash. The chelating agent EDTA enhanced the thermal degradation of PCDD/F, but the addition of Na₂HPO₄ in chelated fly ash as an inhibitor promoted PCDD/F regeneration. Further, there is a variable output of dioxins and corresponding I-TEQs under different temperatures and reaction times; however, longer reaction duration and higher temperatures proved highly effective. The overall toxicity of all thermally tested fly ashes was lesser than the permissible value of 50 ng I-TEQ/kg for resource utilization and observed in the range of 1.84 ± 0.15 to 19.45 ± 0.89 ng I-TEQ/kg. The investigation of the PCDD and PCDF signatures suggests that thermal destruction was a major pathway of degradation by breakage of the C-O bond, compared to dechlorination as observed by a high percentage contribution of HpCDD/F and OCDD/F congeners in thermally treated fly ashes. Low-temperature pyrolysis is an auspicious disposal technology that requires additional studies for large-scale applications.