Determination of operation parameters for magnesium-air fuel cell to recover nitrogen and phosphorus from wastewater

Recovering phosphorus (P) and nitrogen (N) from wastewater not only contributes to environmental protection but also aligns with sustainable development goals. This study employed a magnesium-air fuel cell (Mg-O₂-FC) to extract P and N from wastewater in the form of struvite (MgNH₄·6H₂O), based on the removal efficiency of ammonia and phosphate, electricity generation capacity and struvite purity to determine the optimal operation parameters. These parameters included hydraulic retention time (HRT), service life of magnesium sheet, and precipitation discharge frequency. The results showed that the removal efficiency of ammonia from 0 to 4h was 55.99%, and that from 4 to 12h was only 15.74%. The phosphate removal efficiency in the initial cycle was 97.68% but decreased to 63.25% after 24h. The phosphate removal rate in 2 min increased by 145% when the precipitation discharge frequency increased from 4 h/time to 24 h/time. Consequently, the HRT, service life of the magnesium sheet, and precipitation discharge frequency were selected as 4 h, 24 h, and 24 h/time. These optimized conditions provide valuable insights for the practical implementation of Mg-O₂-FC in recovering N and P from wastewater.