Perfluoroalkyl and Polyfluoroalkyl Substances Release from Biosolid-Derived Compost

This study investigated the release potential and controlling mechanisms of representative per- and polyfluoroalkyl substances (PFAS) of varying carbon-chain lengths from a commercial biosolid-derived compost using sequential leaching with water and saline solutions (10 mM NaCl and 5 mM CaCl(2)). The compost contained >40% organic matter, PFAS concentrations up to 140 ng·g(-1), and precursor levels below 5 ng·g(-1). Eluate analyses revealed dissolved organic matter (DOM) concentrations up to 1400 mg·L(-1) and major ions (Ca, Mg, Na, K, Cl, P, and S) reaching 600 mg·L(-1), accompanied by PFAS concentrations up to 2600 ng·L(-1). PFAS desorption followed a biphasic patternrapid release within the first hour followed by a slower, sustained phase over 48 hwell described by a first-order two-compartment model with rate constants k (1) = 1-7 h(-1) and k (2) = 0.001-0.016 h(-1). Electrostatic interactions dominated the desorption process, as both Na(+) and Ca(2+) reduced the fraction of fast-release sites (F (1)), with Ca(2+) showing a stronger suppression due to cation bridging and charge screening. Perfluorohexanoic acid (PFHxA) and perfluorohexanesulfonic acid (PFHxS) were almost completely released within 1 h, whereas perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid (PFBS), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonate (PFOS) exhibited prolonged desorption associated with interactions with solid organic matter and DOM. DOM-facilitated desorption was evident, as PFAS-DOM complexation enhanced release under certain ionic conditions. Overall, the results reveal the intricate coupling among compost matrix properties, PFAS molecular structure, and eluent chemistry governing PFAS mobility.