<p>Perfluorocarboxylic acids exhibit chain-length dependent partitioning behavior in sludge matrix based on their structural characteristics, posing a challenge to their removal in wastewater treatment plants. This paper investigates the partitioning mechanism of perfluorocarboxylic acids with carbon chain lengths ranging from short to long (5 to 11 carbons) in activated sludge, return activated sludge, and waste activated sludge, focusing on the influence of perfluorocarboxylic acids structural properties and sludge content and physicochemical characteristics. Longer-chain perfluorocarboxylic acids mainly partitioned into the solid phase of all sludge types, whereas short-chain perfluorocarboxylic acids remained predominantly in the liquid phase. Proteins within extracellular polymeric substances in sludge played a crucial role in perfluorocarboxylic acids partitioning into the solid phase, with spectral shifts in amide I and II bands suggesting perfluorocarboxylic acids-protein binding. Long-chain perfluorocarboxylic acids primarily interacted with EPS proteins via hydrophobic interactions, while short-chain perfluorocarboxylic acids initially exhibited hydrophilic binding, transitioning to hydrophobic interactions at higher concentrations. Among the sludge types, AS exhibited the strongest dependency of partitioning coefficient on perfluorocarboxylic acids chain length. Additionally, sludge characteristics, including total solids and divalent cations (Ca²⁺, Mg²⁺), significantly influenced perfluorocarboxylic acids partitioning by reducing electrostatic repulsion and promoting particle aggregation. These findings provide valuable insights into perfluorocarboxylic acids partitioning behavior in sludge and offer guidance for optimizing sludge management strategies.</p>