An iron-air fuel cell system towards concurrent phosphorus removal and resource recovery in the form of vivianite and energy generation in wastewater treatment: A sustainable technology regarding phosphorus

Abstract

Phosphorous (P) recovery from industrial wastewaters solves both P deficiency and P pollution problems. A sequencing batch iron-air fuel cell was set up to recover P from synthetic wastewater containing 0.6 g-P/L Na₂HPO₄. In the cell, ferrous iron goes into the liquor from iron-anode to precipitate soluble P and form vivianite. Electrons travel from iron-anode to air-cathode through external circuit thus to generate energy. During 3 months' continuous operation, the P removal efficiency stably achieved at around 97.6%, and the average output voltage of cell was 404 mV. After long time operation, performance degradation of iron-air fuel cell was observed due to the electrode passivation caused by the accumulation of P precipitate on the iron-anode surface. The precipitate layer on the iron-anode impeded, but it did not block the mass transfer of ferrous iron to the anode liquor. The cell still worked with 25% decrease of output voltage, 86% decrease of current density, 87% decrease of power density and 9 times increase of internal resistance. Further analyses by XRD, FITR and Mössbauer illustrated that vivianite was the main component in both precipitates on the iron-anode surface and at the bottom of anode chamber with respective content of 66% and 30%. Vivianite on the iron-anode surface was a preferable choice due to higher content for P recovery. The iron-air fuel cell system could be a feasible option for achieving the multiple goals of P pollution control, resource recovery as vivianite, and energy generation, thereby contributing to the sustainable development of wastewater treatment.

Keywords: Energy generation; Iron-air fuel cell; Phosphorous recovery; Vivianite.