[Effect of Nitrogen on Magnesium Modified Biochar Adsorption to Phosphorus]

The effect of ammonia-nitrogen in water on phosphorus removal by magnesium modified biochar (MBC) was developed to increase the utilization of wetland plants. The crystal structures were measured by X-ray powder diffraction (XRD). MBC was prepared using reed as the biomass feedstock, which was modified with magnesium chloride. The raw biochar (BC) was prepared as a control. The removal of phosphate from solution using four different methods, i.e. MBC, BC, BC, and MgCl₂ solutions (BC+Mg²⁺) and MgCl₂ solutions (Mg²⁺), under different nitrogen to phosphorus molar ratios and initial phosphorus concentrations was investigated in batch experiments. The results demonstrated that the phosphorus removal efficiency of the four treatment methods, which followed the order of MBC>>BC+Mg²⁺≈Mg²⁺>BC. NH₄⁺ in the solution, promoted phosphorus removal by MBC. In addition, the larger the ratio of nitrogen to phosphorus and the higher the initial phosphorus concentration, the stronger the phosphorus removal capacity of MBC was. In the three treatments with MBC, BC+Mg²⁺, and Mg²⁺, the XRD analysis showed that NH₄⁺ reacted with Mg²⁺ and PO₄^3- in the solution to form MgNH₄PO₄·6H₂O at N:P=5 or 10, promoting the removal of phosphorus. For recycling purposes, waste biomass from constructed wetlands could be used to produce MBC and treat polluted water rich in ammonium and phosphate. Moreover, the ammonium-nitrogen promotes the phosphate removal by MBC. The results from this study provide a new theoretical basis and data support for the treatment of water eutrophication.