Redox-active co-pyrolytic carbon enhances electron transfer and mitigates petroleum hydrocarbon hazards in...

Petroleum hydrocarbon contamination poses persistent environmental hazards to soil ecosystems due to its strong hydrophobicity, stability, and ecological toxicity. In this study, a redox-active co-pyrolytic carbon (CPC), prepared from oily sludge and biomass, was applied to remediate petroleum-contaminated soil, with a focus on redox-mediated biodegradation mechanisms. The results showed that CPC significantly enhanced the removal of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons while effectively reducing soil phytotoxicity. At an optimal dosage of 3%, CPC achieved a TPHs removal efficiency of 93.07% after 180 days, with anthracene and pyrene removal reaching 89.03% and 72.45%, respectively. CPC amendment improved soil physicochemical properties, including organic matter content, porosity, and oxidation-reduction potential (ORP), thereby improving soil redox conditions and contaminant bioavailability. Notably, CPC substantially enhanced the electron transfer-related capacity of dissolved organic matter, indicating a strengthened soil redox-mediated electron transport process. This redox enhancement was accompanied by increased activities of oxidative enzymes, particularly polyphenol oxidase and CYP450, facilitating the degradation of aliphatic and aromatic hydrocarbons. Microbial analysis revealed that CPC reshaped community succession by enriching key degraders such as Microvirga, Brevibacillus, and Sphingomonas, which were strongly correlated with redox indicators and degradation efficiency. Structural equation modeling indicated that electron transfer played a central mediating role linking physicochemical regulation, enzymatic activity, and microbial metabolism. Overall, the results suggest CPC can function as an effective redox mediator, providing a sustainable strategy for mitigating the environmental hazards of petroleum-contaminated soils.