Phosphorus Recovery from Wastewater Prominently through a Fe(II)–P Oxidizing Pathway in the Autotrophic Iron-Dependent Denitrification Process

Phosphorus (P) recovery from wastewater can be completed by iron-involved autotrophic denitrification via forming Fe(III)–P precipitates and/or adsorbing P onto Fe(III) oxyhydroxides. However, so far, most studies focused on the final P-containing products, while the P-capturing pathways in such a process remain unclear. In this work, autotrophic iron-dependent denitrification (AIDD) was used as a typical anoxic iron-involved P-capturing biosystem to investigate the main P recovery pathways. The AIDD biosystem showed a relatively stable capability of capturing P coupled with nitrate reduction. Direct formation of amorphous Fe(II)–P precipitates after the phosphate was fed, followed by microbially driven oxidation into Fe(III)–P minerals, was found to be the primary pathway for the P capture. In addition, adsorption of phosphate onto the formed iron oxyhydroxides also contributed to the P recovery. This work provides better understanding about recovering P in AIDD and iron-involved denitrification and highlights the important roles of iron oxidizers in the iron-related biological wastewater treatment processes.