Magnetically modified fungal Mn oxides with high sequestration efficiency for simultaneously removing multiple heavy metal ions from wastewater

Environmental contamination from metals involved in industrial processes has become a serious concern, and new methods are needed to prevent their release and accumulation. In this study, we investigated the efficiencies of magnetically modified biogenic manganese oxides (MMBMOs) for simultaneously sequestering Cd²⁺, Co²⁺, Ni²⁺, and Co ²⁺ in the presence and absence of extra Mn²⁺. A Mn(II) oxidizing fungus, Acremonium strictum strain KR21-2, was employed to easily generate stable aggregations of BMO, fungal hyphae and a commercial available magnetite powder. A majority of the MMBMO aggregates (>99%) was magnetically recovered when formed with 55 mg/L Mn(II) and ≥50 mg/L magnetite powder. MMBMOs newly formed effectively sequestered heavy metal ions with high efficiency (>97%) upon repeated treatments and were subsequently almost completely trapped (>96%) using applied magnetic fields. Extra Mn ²⁺ added to these mixtures was readily oxidized to Mn oxide, providing additional sorption sites and resulting in higher sequestration efficiency compared no extra Mn²⁺. Inactivating the MMBMO-associated Mn(II) oxidase by heating MMBMOs at 85 °C for 1 h resulted in lower sequestration efficiency. The results presented here demonstrate that enzymatically active MMBMOs are potentially useful biogenic materials for remediating and recovering heavy metal ions from wastewater at ∼mg/L levels.