RESUMEN
To study the effect of biomass particle size on the rate and ability of phosphorus removal from aqueous solution by MgO-loaded Phragmites australis biochar (MBC), MBC was prepared using 0.0-0.5, 1.0-2.0, and 6.0-8.0 mm Phragmites australis particles as the feedstock and MgCl2 as the modification material. The MBC was characterized using FTIR, XRD, and SEM techniques. Kinetic and isotherm experiments of phosphate (PO43--P) adsorption from aqueous solution by the MBC were conducted, and the experimental data were fitted with various kinetic and isotherm models. The results showed that the adsorption rate of PO43--P by the MBC increased with the increase in biomass particle size. The amount of PO43--P adsorbed by the MBC prepared from 0.0-0.5, 1.0-2.0, and 6.0-8.0 mm particles reached 15.4%, 25.8%, and 80.8%, respectively, within 2 h. The biomass particle size did not affect the maximum PO43--P adsorption capacity (249.0-254.7 mg·g-1) of the MBC. MBC prepared from the 6-8 mm particles retained the complete cell wall structure of the Phragmites australis, and a large number of micropores and mesopores were generated during pyrolysis, thereby forming a hierarchical, regular, and well-connected pore structure. MBC prepared from the 0.0-0.5 mm and 1.0-2.0 mm particles had inferior pore structures with inferior pore connectivity, which affected the diffusion rate of PO43- ions inside the MBC and limited the PO43--P adsorption rate. Therefore, when using waste Phragmites australis harvested from a constructed wetland to produce MBC and remove phosphorus from water, the Phragmites australis should be crushed into 6-8 mm particles. Over-crushing deteriorates the pore structure of the produced MBC and reduces the removal rate of phosphorus by the MBC.
RESUMEN
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 PO43- 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.