Emission of Per- and Polyfluoroalkyl Substances from a Waste-to-Energy Plant─Occurrence in Ashes, Treated Process Water, and First Observation in Flue Gas

Abstract

Per- and polyfluoroalkyl substances (PFASs) are a large group of compounds commonly used as industrial chemicals and constituents of consumer products, e.g., as surfactants and surface protectors. When products containing PFASs reach their end of life, some end up in waste streams sent to waste-to-energy (WtE) plants. However, the fate of PFASs in WtE processes is largely unknown, as is their potential to enter the environment via ash, gypsum, treated process water, and flue gas. This study forms part of a comprehensive investigation of the occurrence and distribution of PFASs in WtE residues. Sampling was performed during incineration of two different waste mixes: normal municipal solid waste incineration (MSWI) and incineration of a waste mix with 5-8 wt % sewage sludge added to the MSWI (referred to as Sludge:MSWI). PFASs were identified in all examined residues, with short-chain (C4-C7) perfluorocarboxylic acids being the most abundant. Total levels of extractable PFASs were higher during Sludge:MSWI than during MSWI, with the total annual release estimated to be 47 and 13 g, respectively. Furthermore, PFASs were detected in flue gas for the first time (4.0-5.6 ng m^-3). Our results demonstrate that some PFASs are not fully degraded by the high temperatures during WtE conversion and can be emitted from the plant via ash, gypsum, treated process water, and flue gas.

Keywords: PFASs; bottom ash; fly ash; municipal solid waste; waste incineration.

Figure 1

Overview of the waste incineration plant, with sampling points indicated by gray arrows.

Figure 2

Content of PFASs in waste incineration residues. Circle radii denote the average concentration in the sample matrix. APCR: air pollution control residue.

Figure 3

Mass flows on an annual basis, based on the findings in this study, of PFASs from the waste-to-energy plant presented by the respective residue stream. Gypsum is not shown due to negligible quantities. MSWI: municipal solid waste incineration. *Release of PFASs from waste storage is described in Björklund et al.