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Biosolids (stabilised sewage sludge) are the final solid residues of the wastewater treatment process and are generally applied on agricultural land in many countries, including Australia. Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic fluorinated chemicals with ubiquitous applications in consumer products and persist in the environment. Globally, PFAS have been detected in biosolids and are considered a source of PFAS discharge to the environment. The thermal treatment of biosolids is gaining increasing interest in the water sector. Therefore, the viability of thermal techniques for the safe destruction of PFAS has received substantial research attention in the last few years. Recent studies suggest that PFAS in biosolids can be removed and potentially destroyed during combustive (such as incineration) and non-combustive thermal treatment, such as pyrolysis, gasification, and hydrothermal carbonisation/liquefaction. However, there is limited understanding on the fate and transformation of PFAS degradation products across the overall thermal treatment process from biosolids feed pre-treatment to the gas cleaning (post-thermal treatment) stage. This review consolidates the current knowledge on PFAS transformation, destruction, and final fate before, during, and after thermal treatment of biosolids, covering lab, pilot scale, and industrial studies. It is suggested that PFAS degradation mechanisms during thermal treatment of biosolids may differ from the established pathways for pure PFAS salts, given that biosolids have a complex organic and inorganic matrix and typically have low PFAS concentrations. Among all thermal treatment techniques, pyrolysis has received extensive investigations at different scales of operation. However, for all techniques, treatment temperatures and residence time need to be sufficiently optimised for designing realistic large-scale thermal systems relevant to biosolids' compositional peculiarities for PFAS destruction.
Hakeem et al. (Fri,) studied this question.