Microbial-induced reassembly of phosphate sol: New insight into the removal and fixation of divalent manganese in natural aquatic environment.

The commonly used precipitation method struggles to effectively remove low-concentration heavy metals from water. Herein, we demonstrate that the formation of non-settleable phosphate sols at a low low-concentration is the main reason by using phosphate precipitation as an example and report a new method called microbial-induced reassembly (MIR) of the phosphate sols for the removal and fixation of divalent manganese (Mn(II)) from low-concentration wastewater under neutral conditions. Under the induction of microorganisms, the Mn₃(PO₄)₂ sols formed in low Mn(II) concentration could be reassembled into larger and flower-like precipitates with good settleability, allowing for the removal and fixation of low-concentration Mn(II) through natural settlement. Moreover, MIR is able to reduce Mn(II) levels from 10 mg/L to as low as 0.1 mg/L, achieving nearly 100% removal. The interaction between bacterial protein functional groups and Mn²⁺ ions drives the reassembly of Mn₃(PO₄)₂ sols. MIR of phosphate sol is applicable to both Gram-negative bacteria, such as Escherichia coli, and Gram-positive bacteria, such as Staphylococcus aureus, as well as mixed aerobes. It is also suitable for the removal and fixation of other heavy metals like copper and zinc. This study offers a novel approach for the removal of low-concentration heavy metals from water, more importantly provides a new insight into the migration and fixation of heavy metals in the form of phosphate precipitates induced by microbes in natural aquatic environments.