Variation of PCDD/Fs and Their Monomer Components During Low-Temperature Thermal Decomposition (250–500 °C) of Municipal Solid Waste Incineration Fly Ash

• • Optimal low-temperature pyrolysis conditions for PCDD/F removal from MSWI fly ash are 380 °C for 1.0 h, achieving degradation rates of 97.8% for PCDDs and 97.6% for PCDFs, which is critical for meeting stringent emission standards and reducing toxic equivalency. • • Pyrolysis temperature exerts a dominant influence on PCDD/F removal, with influence weights of 20.86 (mass) and 21.41 (TEQ), compared to time weights of 4.27 and 3.36, indicating that precise temperature control is more critical than duration for process efficiency. • • At 250–300 °C, PCDD/F concentrations increase synchronously, highlighting a dangerous window where de novo synthesis or precursor reactions dominate; this necessitates avoiding this temperature range in industrial practice to prevent inadvertent formation. • • At 300 °C for 2.0 h, dechlorination of high-chlorinated congeners significantly elevates 2,3,7,8-T4CDD (I-TEF=1.0) and 1,2,3,7,8-P5CDD (I-TEF=0.5), which are major TEQ contributors, underscoring the need for temperatures above 350 °C to ensure destruction rather than transformation.