Improved humification and Cr(VI) immobilization by CaO₂ and Fe₃O₄ during composting

The current research studied how Fe₃O₄ nanomaterials (NMs) and CaO₂ affect humification and Cr(VI) immobilization and reduction during the composting of oil-tea Camellia meal and Cr-contaminated soil. The results showed that Fe₃O₄ NMs and CaO₂ successfully construct a Fenton-like reaction in this system. The excitation-emission matrix-parallel factor (EEM-PARAFAC) demonstrated that this Fenton-like treatment increased the generation of humic acids and accelerated the humification. Meantime, RES-Cr increased by 5.91 % and Cr(VI) decreased by 16.36 % in the treatment group with CaO₂ and Fe₃O₄ NMs after 60 days. Moreover, the microbial results showed that Fe₃O₄ NMs and CaO₂ could promote the enrichment of Cr(VI) reducing bacteria, e.g., Bacillus, Pseudomonas, and Psychrobacter, and promote Cr(VI) reduction. This study gives a novel view and theoretical reference to remediate Cr(VI) pollution through composting.