Thermal desorption behavior of Benzo(a)pyrene (BaP) in contaminated soil under different biochar treatments

Persistent organic pollutants like Benzo(a)pyrene (BaP) at redeveloped industrial sites pose significant ecological risks, making soil remediation urgently necessary. Thermal desorption is an effective method for removing BaP from contaminated soils, but its broad application is hindered by high energy demands. Biochar has been recommended as a promising catalyst due to its porous structure and surface functional group for enhancing thermal desorption. However, the mechanisms by which biochar promotes pyrolysis and facilitates BaP remediation are not fully understood. In this study, biochars were produced from three agricultural wastes, including straw (SB), twig (TB), and peanut shell (PB), to evaluate their effectiveness on the removal of BaP. The research focused on how temperature, treatment duration, and biochar application rates influence BaP removal. Results demonstrated that SB at 10% application ratio significantly improved removal efficiency under lower temperatures (300 °C) and shorter treatment times (10 mins). Under these conditions, BaP removal reached 62%, compared to only 12% in control samples. Nevertheless, biochar inhibited BaP removal as the treatment duration increased to 30 and 60 mins, indicating its adsorbent effects. Furthermore, biochar altered pyrolysis pathways and reduced the formation of toxic derivatives, with highest performance found in TB. A 5% biochar addition effectively suppressed toxic derivatives at higher temperatures (500 °C), while a 10% rate achieved similar results at lower temperatures (300 °C). Overall, these findings highlight the dual function of biochar as an adsorbent and catalyst, providing a scientific basis for optimizing thermal remediation strategies while minimizing secondary pollution.