Pinewood Biochar as an Affordable Adsorbent for Short- and Medium-Chain PFAS Removal from Contaminated Water

The present paper investigates the adsorption performance of pinewood-derived biochars produced at two pyrolysis temperatures (850 °C, PW-A; 1000 °C, PW-B), including sieved fractions (PW-A1 and PW-A2) and a functionalized variant (PW-C), for the removal of five short- and intermediate-chain PFASs (PFBA, PFBS, PFHxA, PFHxS, and GenX) from water under continuous-flow conditions. Adsorption behavior was evaluated using Freundlich and Hill isotherm models. The Hill model provided a superior fit for most PFAS–adsorbent systems, highlighting the importance of cooperativity effects, particularly for short-chain PFASs. In single-compound experiments, PFBS and GenX showed the highest adsorption capacities (up to 82.3 and 68.5 mg g−1), while PFBA and PFHxA exhibited the lowest. Among the tested materials, biochar produced at 1000 °C (PW-B) consistently demonstrated the highest adsorption efficiency. Compared to activated carbon, PW-B showed comparable performance for PFBA, PFBS, PFHxA and PFHxS and significantly better performance for GenX. In mixed-PFAS systems, competitive effects reduced adsorption capacity and cooperativity. Sulfonic PFASs showed higher affinity than carboxylic PFASs, following the trend PFHxS > PFBS > PFHxA > PFBA. Overall, the results demonstrate that waste-derived biochar represents a low-cost and sustainable alternative for PFAS removal in realistic water-treatment scenarios, supporting scalable solutions aligned with global environmental goals.