Short-Chain vs. Long-Chain Per- and Polyfluoroalkyl Substance (PFAS) Removal: A Critical Review of Coagulation and Adsorption Behaviors

Abstract

The global phase-out of legacy long-chain per- and polyfluoroalkyl substances (PFASs) has driven the chemical industry toward short-chain alternatives. However, this shift has created unpredictable treatment challenges due to their different physicochemical behavior. This review systematically compares the removal of long- and short-chain PFASs via coagulation and adsorption. With an octanol–water partition coefficient (log Kow) of 2.31 for perfluorobutanoic acid (PFBA) versus 4.81 for perfluorooctanoic acid (PFOA), short-chain PFASs are more water-soluble and less hydrophobic. Consequently, conventional coagulation achieves <20–30% removal for short chains versus 20–60% for long chains. In granular activated carbon (GAC), short-chain PFAS breakthrough occurs after 6000–11,000 bed volumes and is easily displaced by long-chain PFASs and natural organic matter (NOM). Strong base anion exchange resins (AERs) capture short chains via electrostatic attraction, but competing anions (e.g., 0.1 M CaCl2) reduce adsorption capacity by 94% on average. Spent adsorbents create secondary pollution: PFASs leach from used GAC in landfills, and thermal regeneration leaves behind short-chain fluorocarbons (e.g., CF4) unless temperatures exceed 1400 °C. To address short-chain PFASs without continuing pollution, water management must move beyond hydrophobic first systems toward charge-targeted adsorbents, hybrid-adsorption destruction methods, and life-cycle waste management.