Per- and polyfluoroalkyl substances (PFASs) profile in sludge biosolid fertiliser intended for agricultural use in Japan.

This study investigated the behaviour of per- and polyfluoroalkyl substances (PFASs) during the stabilisation of "sludge fermented fertiliser" from sewage sludge via 90 °C thermal fermentation at a wastewater treatment plant (WWTP) in Japan. Using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS), 42 PFASs were quantified across production stages, with concentrations dominated by sulphonamides and perfluoroalkyl carboxylic acids (PFCAs). The pretreatment stage, which involved mixing dewatered sludge with external materials and matured compost, was identified as a primary contamination source, increasing ∑42PFASs concentrations from 23,000 to 74,000 ng/kg dry weight (dw). Results indicate that the 90 °C fermentation process facilitated the thermal conversion of PFAS precursors into stable terminal perfluoroalkyl acids (PFAAs), leading to a 65% increase in PFAAs concentration, reaching 78,000 ng/kg dw. Perfluorooctanesulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) accounted for 38% and 28%, respectively, of this increase. An unexpected further increase in PFASs concentrations was observed during the final crushing and pelletization stage, likely driven by mechanochemical activation and thermal hydrolysis during pelletisation. These findings highlight the need for immediate source control during pretreatment and more in-depth research into PFASs behaviour during thermal fermentation and final mechanical processing to ensure environmental safety in biosolid recycling.