Municipal waste-to-energy combustion of fluorinated polymers as a potential source of PFOA in the environment
Date
2021
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Widespread detection of perfluorooctanoic acid (PFOA), a persistent organic pollutant, has sparked interest in assessing the degree to which municipal waste-to-energy combustion of fluorinated polymers contributes as a PFOA source in the environment. This study evaluated the potential of fluorinated polymers to emit PFOA under conditions representative of U.S waste-to-energy combustion through a bench-scale experimental program composed of four projects. First, a survey was conducted using a stratified sampling approach to define typical U.S. waste-to-energy facility operating conditions for furnace temperature, gas residence time, oxygen content, and moisture level. Second, a novel bench-scale model reactor system was designed to capture the essential chemistry affecting transformations in the combustion zone above the fuel bed of these facilities, assuring a representative reaction atmosphere in subsequent experiments. Qualification of the bench-scale quartz reactor system verified effective PFOA collection efficiency via absorption in water-filled impingers. Third, side-chain fluorinated polymers (SCFPs) of unknown composition were characterized and assessed for their potential to emit PFOA under conditions representative of municipal waste-to-energy combustion, including exhaust gas hydrogen fluoride levels prior to pollution control. Fourth, fluoropolymers manufactured using the ammonium salt of PFOA were evaluated for their potential to generate PFOA during bench-scale combustion under similar conditions. As in the third project, PFOA was determined in exhaust gas samples (collected via absorption into water) using liquid chromatography with tandem mass spectrometry. Concurrently, mass balance accounting assessed transformation of fluoropolymer organofluorine content into inorganic fluoride to determine the extent of carbon–fluorine bond breakage. ☐ Under conditions representative of municipal waste-to-energy combustion, bench-scale testing determined that waste-to-energy combustion of six distinct fluorinated polymer classes does not emit detectable PFOA (≤54 ng dscm-1). When silicon tetrafluoride formation was prevented during combustion testing, 100% recovery of fluorine input as fluoride ion in the impinger solution verified complete transformation of fluoropolymer organofluorine content to inorganic fluoride. Complete fluoride recovery demonstrated that all carbon–fluorine bonds had been broken, independently confirming that PFOA had not been formed. The results of this study indicate that municipal waste-to-energy combustion of the fluorinated polymers investigated is not expected to be a PFOA emission source in the U.S.
Description
Keywords
Bench-scale, Incineration, Mass balance, Reactor design, Representative conditions