Treatment of sites contaminated with perfluorinated compounds using biochar amendment

• PFC pollution is a serious environmental problem.
• Sorption isotherms of PFOS, PFOA and PFHxS on two biochars were compared.
• Soil amendment with biochar did not have an effect on total PFC sorption.
• AC can be a useful method for in situ remediation of PFC-contaminated soils.

Per- and polyfluorinated compounds (PFCs) have been attracting increasing attention due to their considerable persistence, bioaccumulation, and toxicity. Here, we studied the sorption behavior of three PFCs, viz. perfluorooctanesulfonic acid (PFOS), perfluorooctanecarboxylic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), on one activated carbon (AC) and two biochars from different feedstocks, viz. mixed wood (MW) and paper mill waste (PMW). In addition, we explored the potential of remediating three natively PFC contaminated soils by the addition of AC or biochar. The sorption coefficient i.e. Freundlich coefficients Log KF, (μg/kg)/(μg/L)n, for the two biochars were 4.61 ± 0.11 and 4.41 ± 0.05 for PFOS, 3.02 ± 0.04 and 3.01 ± 0.01 for PFOA, and 3.21 ± 0.07 and 3.18 ± 0.03 for PFHxS, respectively. The AC sorbed the PFCs so strongly that aqueous concentrations were reduced to below detection limits, implying that the Log KF values were above 5.60. Sorption capacities decreased in the order: AC > MW > PMW, which was consistent with the material’s surface area and pore size distribution. PFC sorption to MW biochar was near-linear (Freundlich exponent nF of 0.87–0.90), but non-linear for PMW biochar (0.64–0.73). Addition of the AC to contaminated soils resulted in almost complete removal of PFCs from the water phase and a significant (i.e. 1–3 Log unit) increase in soil–water distribution coefficient Log Kd. However, small to no reduction in pore water concentration, and no effect on Log Kd was found for the biochars. We conclude that amendment with AC but not biochar can be a useful method for in situ remediation of PFC-contaminated soils.