Experimental investigation on PFAS degradation through municipal sludge combustion processes

The incineration of sludge matrices at high temperature (>800 °C) represents a valid solution for per- and polyfluoroalkyl substances (PFAS) abatement. The present study investigates the thermal degradation of sludge samples coming from a municipal wastewater treatment plant, by employing a laboratory-scale continuous bubbling fluidized-bed combustor operating at 850 °C and atmospheric pressure. By utilizing samples of raw municipal sludge and spiked with a known PFAS mixture (up to 8 mg/kg), the research could achieve a high analytical sensitivity, enabling a comprehensive evaluation of PFAS combustion efficiency. Preliminary results elucidated the distribution of PFAS molecules within the combustion byproducts, namely flue gases, fly and bottom ashes, shedding light on the PFAS degradation pathways during incineration. The incineration process was characterized by high combustion efficiency (>96 %). PFAS degradation was always greater than 99.9 % and among them only PFBS, PFOS and PFTeDA were not completely decomposed during the process. The maximum concentration of unconverted PFAS in the flue gas (12 ng/Nm3) was reduced by 6 orders of magnitude compared to the initial one. Moreover, PFAS concentration within the fly ashes was in the order of 8–18 μg/kg, while it ranged between 1–5 μg/kg in the bottom ashes.