Microbial transformation of Fenton sludge to crystalline iron minerals with fermentation-derived phosphorous for...

The reuse of Fenton sludge (FS) for heavy metal immobilization offers a sustainable waste management approach; however, its amorphous structure and limited functional groups hinder adsorption efficiency and stability. This study reports the microbial transformation of FS into crystalline Fe minerals via Fe(III)-reducing bacteria, using fermentation supernatant as a phosphorus source. Phosphate concentration plays a key role in determining mineral formation: low phosphate levels restricted microbial activity and Fe(II) production, leading to magnetite formation, while high phosphate levels enhanced microbial activity and Fe(II) generation, favoring vivianite formation. Biogenic vivianite exhibited rapid adsorption kinetics and significantly higher Pb (200.1 mg g^-1) and Cd (123.9 mg g^-1) capacities compared to the initial FS (15.1 mg g^-1 and 13.9 mg g^-1, respectively). Meanwhile, biogenic magnetite demonstrated superior Cu adsorption at 139.8 mg g^-1, far exceeding that of the initial FS (23.5 mg g^-1). Mechanistic investigations revealed that Pb stabilization occurs via vivianite dissolution-recrystallization, Cd immobilization is driven by surface precipitation, and Cu is incorporated into magnetite through isomorphic substitution. Moreover, biogenic vivianite and magnetite synthesized in a pilot-scale reactor were successfully applied in soil remediation, effectively immobilizing Pb, Cd, and Cu and reducing their mobility.