Removal of manganese in acidic solutions utilizing Achromobacter sp. strain QBM-4 isolated from mine drainage

Biological approaches with the core of manganese-oxidizing bacteria (MnOB) are cheap and environmentally friendly solutions for the removal of bivalent manganese (Mn(II)). These bacteria typically worked well in the pH range of 5.5 – 8.0 but poorly under pH below 5.5. In this study, we isolated an acid-tolerant manganese-oxidizing bacterium (Achromobacter sp. strain QBM-4) from acid mine drainage (AMD), which was effective for Mn(II) removal at pH 4.0. Under optimized treatment conditions (i.e., 60.0 mg·L−1 Mn(II), 100.0 mg·L−1 Fe(III), and 35.0 °C), the Mn(II) removal efficiency reached 93.6 ± 0.8% at an initial pH of 4.0. Approximately 68.0% of the Mn(II) was removed through adsorption, and the remainder was attributed to oxidation. The Mn(II) oxidation rate was ~ 0.05 mM·d−1 (initial pH of 4.0), comparable with other MnOB performing under near-neutral solutions. Ferric ions (Fe(III)) can form amorphous iron hydroxides, facilitating sorptive removal and catalytic oxidation of Mn(II). In contrast, ferrous ions (Fe(II)) reductively dissolve manganese oxides, inhibiting Mn(II) removal. A mechanism for the biological removal of Mn(II) was proposed, and the performance of Achromobacter sp. strain QBM-4 was further verified in three types of mine drainage.