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Efficient municipal solid waste (MSW) management promotes resource conservation, climate-change mitigation, public health, and environmental protection. A key aspect of environmental protection within MSW management is ensuring that potential pollutants are not released into the environment. One group of environmental pollutants of global concern is per- and polyfluoroalkyl substances (PFAS). Also known as “forever chemicals”, these are used in a wide variety of consumer products and industrial processes, and are known for their persistence. The fate of PFAS in waste-management processes, such as Waste-to-Energy (WtE), is largely unknown. This thesis aimed to investigate the fate of PFAS in a WtE plant.

Comprehensive sampling was performed to provide a synoptic overview of the occurrence and distribution of PFAS in residual streams, and to investigate the potential emission of PFAS from the WtE process to the environment.

Short-chain (C ≤ 7) perfluorocarboxylic acids were the dominant class of PFAS across all matrices analysed. PFAS was found in leachate from the temporary MSW stockpile located at the WtE plant, as well as in most incineration residues (e.g., bottom ash, condensate, and flue gas) during the incineration of MSW. Co-incineration of sewage sludge from a wastewater treatment plant and MSW (with the former added at 5–8 wt.% of the latter) led to an increase in the concentration of PFAS in all matrices, with the exception of filter ash and stack flue gas.

In general, the wet flue-gas treatment was able to capture some PFAS and transfer them to the in-house process-water treatment; however, further optimisation is required to increase the ability of this treatment to capture the shortest PFAS investigated (perfluorobutanoic acid).

Overall, these findings highlight that some PFAS are not fully degraded during WtE conversion, and that PFAS could enter the environment via both leaching from unburnt MSW and incineration residues.

This study investigated the fate of per- and polyfluoroalkyl substances (PFAS) in the in-house process-water treatment (PWT) of a 65 MW Waste-to-Energy (WtE) plant. PFAS are used in a wide variety of applications, but are persistent and will end up in waste streams when products reach the end of their lives. The study aimed to identify the pathway of PFAS from flue-gas treatment to the PWT, and to assess the efficiency of the PWT in removing PFAS. Sampling was conducted over five days at five different locations in the PWT. Nine of the eleven target PFAS were detected in at least one sample. The total concentration of PFAS exhibited day-to-day variations, likely caused by fluctuations in the composition of the waste fuel. The highest average PFAS concentration was observed in foam, and was around 130 times that found in the treated water. However, the mass flow of PFAS in the foam was substantially lower, on average 20 times, than that in the treated water. It was found that the condensate scrubber acts as a PFAS transfer step, carrying over certain PFAS from the flue gases into the condensate and PWT. The mass flow rate of PFAS in the PWT after the addition of condensate was six times that before the addition. The study concludes that, while there are some key changes that could be made to enhance the PFAS removal capacity of the in-house PWT, in its current configuration the PWT is not able to efficiently remove PFAS from process-water.

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.

Per- and polyfluoroalkyl substances (PFASs) are a diverse group of chemicals used in consumer products, which will inevitably end up in waste streams. Landfills are widely recognized secondary point sources of PFASs, but other types of waste management sites have received less attention. Therefore, in a case study presented here we investigated releases of PFASs from temporarily stored waste by determining quantities of 34 PFASs in leachate from a Waste-to-Energy stockpile (45 000 ± 2000 tonnes) during five months in 2019. We also measured extractable organofluorine (EOF) to account for PFASs not included in the target list. The mean total concentration of the 34 PFAS (Σ34PFAS) was 211 ± 31 ng/L, and short-chain (C4–C7) perfluorocarboxylic acids (PFCAs) accounted for 56–60% of the total. Moreover, we found that Σ34PFAS only accounted for 12% ± 4% of EOF detected in the leachate. Our results demonstrate that waste stockpiles are previously unexplored sources of PFASs in the environment, and the dominance of short-chain PFCAs is consistent with observed profiles of contaminants in landfill leachates.