Phosphorous removal and high -purity struvite recovery from hydrolyzed urine with spontaneous electricity production in Mg -air fuel cell

In this study, a single-chamber Mg-air fuel cell (MAFC) is used to remove phosphorous (P) and to simultaneously recover struvite and electricity from synthetic hydrolyzed urine. The Mg 2+ generated from the anodic oxidation of Mg alloy provides a source of Mg for struvite precipitation. Meanwhile, the cathodic oxygen reduction re- action through a four-electron pathway produces OH- to maintain suitable pH for struvite precipitation and the avoid the addition of exogenous chemical reagents. The P concentration in the e ffluent is lower than 0.5 mg L-1 after a 15-min treatment and meets the sewage grade A discharge standard in China. The P removal e fficiency of urine reaches 99.48% with an e ffluent P concentration of 0.28 mg L-1 after a 25-min operation of MAFC, and the removed P can be completely recovered as high-purity struvite precipitation. The rate constant for P removal is calculated to be 0.46 min(-1) by fitting a first-order kinetic model. The recovered precipitation is identi fied as struvite, and the chemical analysis reveals a struvite purity of 98.26%. The maximum power density of MAFC with P-containing urine as electrolyte reaches 552.32 mW m(-3) , which is 47.39% higher than that of MAFC with P-free electrolyte. The struvite precipitation reaction can promote the electricity production of MAFC. This work provides not only a novel method for purifying and recovering resources from urine but also a new perspective for enhancing the electrochemical performance of MAFC in the future.