Behavior of nitrite removal and vivianite-based phosphorus recovery with biogenic bivalent iron mediated by iron-reducing bacteria: Competition or sequencing?

Nitrogen and phosphorus removal remains a formidable challenge in traditional wastewater treatment methods. In this study, the iron-reducing bacteria Shewanella oneidensis MR-1 was used to reduce ferrihydrite to form biogenic bivalent iron (Fe(II)). The biogenic Fe(II) can chemically denitrify NO2−-N to achieve nitrogen removal, and can also combine with phosphorus to form a phosphorus recovery product, vivianite (Fe3(PO4)2·8H2O). The start-up stage of accumulating biogenic Fe(II) and the operation stage of utilizing biogenic Fe(II) was established. Batch experiments demonstrated phosphorus and NO2−-N competed for biogenic soluble Fe(II), resulting in the formation of secondary Fe(II) mineral vivianite. Furthermore, the chemical denitrification of NO2−-N with vivianite increased total nitrogen removal from 17 % to 39 % (start-up phase) and 67 % to 77 % (operating phase), respectively. This study demonstrated an effective approach for nitrogen removal and phosphorus sequestration employing biogenic Fe(II), revealing the synergistic interactions between the two processes.