Coupling electrochemical iron dissolution and bio-cathodic denitrification for nutrient removal, vivianite, and energy recovery in an iron-anode microbial fuel cell

Nitrogen (N) and phosphorus (P) compounds are common pollutants in wastewater, and their efficient removal and recovery are essential for sustainable development. Here, a two-chamber iron-anode microbial fuel cell (IA-MFC) was developed for simultaneous nitrate removal, phosphate recovery, and energy generation without external organic carbon. The iron anode continuously released electrons to enhance bio-cathodic denitrification, while the generated Fe²⁺ promoted phosphate precipitation as vivianite. The maximum volumetric removal rates of 0.0259 kg-N/(m3·d) and 0.0529 kg-P/(m3·d) were achieved during the initial operational phase (days 1–4). Meanwhile, the maximum cycle energy recovery reached 26.1 Wh/m³ , with a maximum power density of 0.64 W/m³ . Vivianite was identified as a major Fe–P phase in the deposits recovered from the iron-anode surface, with an estimated content of 117.48 mg/g SS based on the EDTA-extractable Fe fraction. Moreover, in this system, cathodic denitrification was a major kinetic constraint. However, system performance deteriorated progressively with extended operation, rather than remaining stable across cycles. Overall, the IA-MFC demonstrated the feasibility of coupling nitrogen removal, phosphorus recovery, and electricity generation in a self-powered system, while electrochemical and microbial stability still need to be improved in future work.