Enhanced degradation mechanism of pyrene by Fe/Mn-modified biochar immobilized microorganisms under Cd(II)...

To address the issues of low remediation efficiency and microbial toxicity stress in soils contaminated with both Cd(II) and pyrene, this study prepared Fe/Mn-modified biochar from buckwheat hulls, screened pyrene-degrading bacterial strains, and developed an immobilized bacterial agent (PFMBC). Using free-living bacteria (YL) and unmodified biochar-immobilized bacterial agent (PBC) as controls, to investigate their pyrene degradation performance and mechanisms under different Cd(II) concentrations. Carrier properties were characterized using XPS and FTIR, microbial physiological indicators and enzyme activities were measured, and pyrene metabolites were analyzed via GC-MS. The results showed that PFMBC exhibited the best degradation performance, achieving a 77.23% pyrene degradation rate after 15 days under 20 mg/L Cd(II) conditions and 60.09% under 60 mg/L Cd(II) stress, which was significantly superior to the controls. Fe/Mn modification enhances the Cd(II) adsorption and immobilization capacity of biochar, promotes microbial secretion of extracellular polymeric substances(EPS), increases biofilm stability, reduces cell membrane damage and ROS accumulation, significantly boosts the activity of catechol dioxygenase, dehydrogenase, and catalase, accelerates the ring-opening oxidation and metabolism of pyrene, alters the degradation pathway, and reduces the accumulation of recalcitrant intermediate products. This study elucidated the synergistic mechanism by which Fe/Mn-modified biochar-immobilized bacterial agents enhance pyrene degradation under laboratory simulated Cd(II)-pyrene co-contamination conditions. The results offer a laboratory-scale theoretical basis and experimental reference for the remediation of Cd(II)-pyrene co-contaminated soil, whereas its actual field remediation efficiency and environmental applicability remain to be verified in further field investigations.