Concomitant urea stabilization and phosphorus recovery from source-separated fresh urine in magnesium anode-based...

In this study, we investigated the recovery of nitrogen (N) and phosphorus (P) from fresh source-separated urine with a novel electrochemical cell equipped with a magnesium (Mg) anode and carbon-based gas-diffusion cathode. Recovery of P, which exists primarily as phosphate (PO₄^3-) in urine, was achieved through pH-driven precipitation. Maximizing N recovery requires simultaneous approaches to address urea and ammonia (NH₃). NH₃ recovery was possible through precipitation in struvite with soluble Mg supplied by the anode. Urea was stabilized with electrochemically synthesized hydrogen peroxide (H₂O₂) from the cathode. H₂O₂ concentrations and resulting urine pH were directly proportional to the applied current density. Concomitant NH₃ and PO₄^3- precipitation as struvite and urea stabilization via H₂O₂ electrosynthesis was possible at lower current densities, resulting in urine pH under 9.2. Higher current densities resulted in urine pH over 9.2, yielding higher H₂O₂ concentrations and more consistent stabilization of urea at the expense of NH₃ recovery as struvite; PO₄^3- precipitation still occurred but in the form of calcium phosphate and magnesium phosphate solids.