The binding effect of biochar with polycyclic aromatic hydrocarbons and their derivatives: Role in carbon...

Polycyclic aromatic hydrocarbons (PAHs) and their toxic derivatives pose a significant threat to human health and the environment. Conventional remediations, such as chemical oxidation and hydrothermal treatments, are costly and generate secondary toxic byproducts, limiting their field applicability. This review aims to discuss the dual role of biochar as a cost-effective sorbent to remediate PAHs, and simultaneously provide an environment for PAH-degrading and carbon-sequestering microbial communities. Nonetheless, PAHs are released with pyrolysis gases during biochar production, which usually condense in the porous structure of biochar, having limited bioavailability. Furthermore, biochar engineering strategies such as wood ash amendments to feedstock and controlled pyrolysis conditions (350-550°C) in a vapor-solid separation chamber have been proposed to minimize PAHs contamination in biochar. This review elucidates hydrophobic interactions, pore-filling mechanisms, and π-π electron donor-acceptor interactions as dominant mechanisms for PAH sorption and long-term stabilization in soil. Quantitative evidence revealed that copper-modified Arundo donax and rice husk biochar exhibited high phenanthrene removal efficiencies (94.0-97.6%). Furthermore, rice husk biochar and immobilized bacteria removed 95.50% of phenanthrene and 73.78% of benzo[a]pyrene. Despite progress in safe biochar synthesis and PAHs removal from soil, limited research has addressed the remediation of PAH derivatives, which remains a critical knowledge gap. Therefore, future research should focus on designing multifunctional biochar, along with defined consortia of PAH-degrading and carbon-sequestration microbes to simultaneously enhance sorption and microbial degradation of PAH derivatives for long-term carbon stabilization in subsoil under field conditions.