Biochar-mediated sustainable remediation of petroleum-contaminated soil: From total petroleum hydrocarbon degradation to microbial responses

Biochar (BC)-mediated Fenton-like processes have exhibited outstanding potential in soil remediation. However, the influence of oxidant types and oxidation pathways remains largely overlooked. This study systematically compared the remediation performance, mechanistic pathways, and microbial responses of peroxymonosulfate (PMS) and peroxydisulfate (PDS) activated by Acanthopanax senticosus–derived biochar (ASBC) in petroleum-contaminated soil. Under optimal conditions, the ASBC/PMS system exhibited a higher initial degradation efficiency of total petroleum hydrocarbons (TPHs) (58.8%) than ASBC/PDS (48.1%). In contrast, long-term remediation revealed a superior final TPH removal efficiency in the ASBC/PDS system (68.0%) after three months, exceeding that of ASBC/PMS (59.4%). Mechanistic analysis revealed that TPH degradation in the ASBC/PMS system was dominated by radical-driven oxidation, whereas the ASBC/PDS system primarily proceeded via a nonradical, surface complex–mediated electron transfer pathway. These distinct oxidation mechanisms elicited markedly different microbial responses: radical-intensive conditions impaired the survival of petroleum-degrading bacteria, whereas nonradical oxidation preserved microbial resilience and activity. Consequently, although both treatments ultimately enriched Firmicutes-dominated communities, the nonradical ASBC/PDS system promoted faster microbial recovery and enhanced biodegradation potential. Moreover, both systems effectively alleviated soil phytotoxicity; notably, ASBC/PDS system exhibited superior pH buffering capacity and greater resistance to inorganic anion interference. Collectively, this study reveals that oxidant selection and oxidation pathway critically regulate the coupling of chemical oxidation and microbial processes, highlighting nonradical biochar-activated oxidation as a promising avenue for synergistic soil remediation and bioremediation.