Quadratic and higher-order polynomial (HOP) regression was used for RSM. The independent variables included pH, adsorbent dose (g/L), temperature (°C), initial concentration (C0, mg/L), BET surface area (m²/g), and physicochemical properties of PFAS compounds such as pKa, log Kow, molecular weight (mg/mmol), and Abraham solvation parameters (A, B, S, E, V). These variables were selected based on their relevance to adsorption mechanisms and their established influence on PFAS adsorption.