Application of Fe/Mn-modified biochar immobilized microorganisms in the remediation of pyrene-contaminated soil under Cd(II) coexistence

To address pyrene and Cd(II) co-contamination in soil, an efficient pyrene-degrading bacterial strain J3 was isolated from oil-containing sludge. J3 achieved a pyrene degradation rate of 26.52% within 15 days at an initial concentration of 100 mg/L, and exhibited good tolerance to 20 mg/L Cd(II). Buckwheat husk biochar was used as the carrier; after Fe/Mn modification, the resulting biochar (FMBC) possessed a high specific surface area (348.18 m2/g) and a rich pore structure. FMBC immobilized J3 to form the microbial agent PFMBC. A 180-day soil remediation experiment systematically evaluated PFMBC’s performance. The results showed that PFMBC degraded 76.55% of pyrene, significantly higher than free bacteria and other treatment groups. Moreover, PFMBC stabilized soil pH and redox potential, enhanced the activities of acid phosphatase, urease, and dehydrogenase, and promoted soil organic matter mineralization. Microbial community analysis revealed that PFMBC significantly increased bacterial diversity, enriched genera associated with PAH degradation, and enhanced microbial metabolic and remediation-related functions. These findings provide a reference for the efficient and sustainable bioremediation of soils co-contaminated with PAHs and heavy metals.