Microbially mediated synthesis of vivianite by Desulfosporosinus on the way to phosphorus recovery †

We explored the role of biomineralization in industrial waste sludge formation, using the laboratory cultivation of Desulfovibrio sp. OL sulfate reducing species isolated from the Komsomolsky waste sludge (Russia). The most frequently reported sulfate-reducing bacteria (SRB) biomineralization products are various iron sulfides. Here we present first studies of the products of Desulfosporosinus metallidurans, acidophilic SRB from acid mine drainage. We analyzed the biomineralized sample using X-ray diffraction, electron microscopy, X-ray absorption and Mössbauer spectroscopies, and magnetization measurements via First-Order Reversal Curve (FORC) diagram analysis. Our findings show that the biomineralization occurring under pure culture conditions leads to the formation of greigite (Fe₃S₄) nanorods, along with larger microbially mediated crystals of vivianite (Fe₃(PO₄)₂·8H₂O) and siderite (FeCO₃). Energy dispersive X-ray spectroscopy revealed that the crystal sizes of vivianite and siderite were comparatively larger than those of the nanorod-shaped greigite. Transmission electron microscopy and Mössbauer spectroscopy detected ultrafine ferrihydrite (Fe₂O₃·nH₂O) superparamagnetic nanoparticles with an average size of 2.5 nm. FORC analysis showed significant magnetic interactions among these nanoparticles, suggesting their potential for magnetic separation applications. The current study demonstrates that ferrihydrite nanoparticles have a strong magnetic affinity for other crystal phases produced by Desulfosporosinus metallidurans. Therefore, we believe that the investigated bacterial species can be exploited in advanced magnetic separation techniques. This offers a cost-effective and environmentally friendly method for purifying sediments in industrial waste sludge.