Influence of pyrolysis temperature on pistachio shell biochar for enhanced PFOA removal from wastewater: A sustainable approach to PFAS remediation

Perfluorooctanoic acid (PFOA) is a persistent pollutant in water, posing significant health risks due to its bioaccumulation and toxicity. This study investigates the effective removal of PFOA using pistachio shell-derived biochar (PS-BC), with an emphasis on optimizing pyrolysis temperature. Among the tested materials, biochar produced at 900 °C (BC-900 °C), with a surface area of 687.87 m²/g, exhibited superior adsorption performance. At an initial PFOA concentration of 4 mg/L and pH 5, BC-900 °C achieved over 99 % removal efficiency at a dosage of 1 g/L within 2 h. The maximum Langmuir adsorption capacity was determined to be 41.07 mg/g. Kinetic studies showed the adsorption followed a pseudo-first-order model (R² = 0.9825), indicating a physisorption mechanism. Adsorption isotherms were best described by the Liu model (R² = 0.9398), suggesting a heterogeneous adsorbent surface with sites of varying affinities and finite adsorption capacity. Thermodynamics indicated that adsorption is spontaneous and endothermic. BC-900 °C also demonstrated strong regeneration potential, maintaining approximately 94 % efficiency over five adsorption-desorption cycles. Its performance remained stable across a broad ionic strength range, with removal efficiencies from 94.3 % to 92.9 % in NaCl concentrations between 0.001 M and 0.1 M, underscoring robustness under varying salinity. Co-existing ions had minimal effect on removal performance, confirming selectivity. Notably, BC-900 °C achieved high PFOA removal at both 1 and 10 mg/L concentrations in complex real wastewater from a nearby food industry, demonstrating practical applicability. These results highlight BC-900 °C as a sustainable, cost-effective, and high-performance adsorbent for PFOA remediation in water treatment systems.