Phosphorous/ammonia recovery and electricity production by using magnesium-air fuel cell electrocoagulation

Abstract

This research compared the removal efficiencies of phosphorus and electricity production when using magnesium-air fuel cell electrocoagulation according to the concentrations of phosphorus and chlorine, based on a investigation of major principles on the effect of NaCl and KH2PO4 concentrations on struvite recovery. The weight ratio of N: P in the synthetic wastewater was 1.2-21. The concentration of NH4Cl was fixed at 0.277 M, and the difference of PO4-P was in the range of 0.006-0.1 M. In addition, the concentration of NaCl as the electrolyte was also compared by 0, 0.01, and 0.1 M, respectively. The removal of phosphorus linearly increased to about 1.1 mol mol-1, depending on the Mg: P ratio, regardless of the initial concentration of phosphate and NaCl. The one-to-one reaction of phosphate and dissolved Mg ions resulted in phosphate removal along with the production of one-on-one magnesium / phosphate minerals such as struvite. In the experiment without NaCl, the average removal rate of phosphorus was 4.19 mg P cm-2 h-1, which was relatively lower than that of the experiment in which NaCl was 0.01 and 0.1, and at that time the average removal rate of phosphorus was 5.35 and 4.77 mg P cm-2 h-1 respectively. The dissolution rate of Mg by electro-oxidation determined the rate of phosphorus removal by struvite recovery. KH2PO4 The average removal rates of phosphorus with dose concentrations of 0.006, 0.01 and 0.02 M increased to 4.02, 5.54 and 6.9 mg P cm-2 h-1, respectively, in proportion to the increase in KH2PO4 dose. However, in experiments conducted under the condition of KH2PO4 of 0.05 and 0.1 M, the average phosphorus removal rate decreased to 4.84 and 2.51, respectively. In the power production part, the maximum power was 25.1 W / m2 at 0.05 M KH2PO4 0.277 M NH4Cl, 26.4 W / m2 at 0.01 M NaCl 0.05 M KH2PO4 0.277 M NH4Cl, 33.2 W / m2 at 0.1 M NaCl 0.05 M KH2PO4 0.277 M NH4Cl. and NaCl Density, and increasing the NaCl concentration under each condition increases the maximum power density and current density. when we Compared about difference of KH2PO4 concentration, the maximum power density was increased in proportion to the increase of the KH2PO4 dose under the condition of 0.05 M, while the condition of 0.05 M or more resulted in the decrease of the maximum power density. In addition, considering the fact that ammonium is consumed in struvite formation, the electricity production and phosphorus / ammonium removal efficiency are compared by difference of ammonium concentration. Ammonium was removed by up to 15%, and all of the phosphorus was removed under the condition that NH4Cl concentration was over 2000 ppm. At this time, ammonium is discharged as NH3 gas simultaneously with formation of struvite, which was recovered by using boric acid. The other condition were fixed at NaCl 0.01 M, PO4 950 ppm.