Low-temperature hydrothermal oxidation of PCDD/Fs in MSWI FA: Performance and regulation mechanisms of Fenton and persulfate systems.

Municipal solid waste incineration fly ash (MSWI FA), classified as hazardous waste, contains highly toxic dioxins (PCDD/Fs). Although conventional high-temperature treatments can achieve complete PCDD/Fs decomposition, they suffer from high energy consumption and potential secondary pollution risks. This study developed a low-temperature hydrothermal advanced oxidation process utilizing Fenton and persulfate systems to efficiently degrade PCDD/Fs in MSWI FA. The Fenton reaction effectively degraded PCDD/Fs, reducing PCDDs and PCDFs concentrations by 35.6% and 14.93%, respectively. The synergistic use of sodium carbonate and ethanol further reduced the toxicity equivalent by 44.58%. The persulfate system demonstrated superior degradation efficiency: under thermal activation at 120 °C, sulfate radicals (SO4-·) were generated, leading to a 63.40% reduction in total PCDD/Fs concentration and a 68% decrease in toxicity equivalent, reaching 667.10 ng I-TEQ/kg. Ethanol exhibits differentiated reaction mechanisms under different systems and temperature conditions. It enhanced PCDD/Fs degradation by improving their solubility in the hydrothermal environment and increasing the contact efficiency between free radicals and the target pollutants. Besides, ethanol converted into hydrogen-donating intermediates like acetaldehyde, thereby promoting the dechlorination of PCDD/Fs. Moreover, heavy metal leaching from the treated residues met national regulatory limits (GB 5085.3-2007). By elucidating the distinct radical-driven mechanisms and synergistic regulatory roles of reagents, this work establishes a pioneering low-temperature hydrothermal strategy. This technology not only clarifies optimized PCDD/Fs degradation pathways but also achieves efficient detoxification while significantly minimizing energy consumption and secondary pollution risks compared to conventional treatments, offering an innovative and practical solution for the harmless treatment of MSWI FA.