Mg/Fe Layered Double Hydroxide Modified Biochar for Synergistic Removal of Phosphate and Ammonia Nitrogen from Chicken Farm Wastewater: Adsorption Performance and Mechanisms

The development of an economical and efficient method for recovering phosphate (PO43−-P) and ammonium nitrogen (NH4+-N) is of paramount importance for environmental remediation. The preparation of Mg/Fe-loaded biochar (Mg/Fe-BC) was achieved through chemical precipitation followed by pyrolysis in this study. Single solution adsorption studies indicated that temperature significantly affected how effectively Mg/Fe-BC could adsorb and remove NH4+-N, whereas PO43−-P adsorption showed minimal temperature sensitivity. In mixed simulated solutions, In the mixed simulated solution, the maximum adsorption capacities of Mg/Fe-BC for PO43−-P and NH4+-N were 145.97–153.05 mg/g and 112.63–121.51 mg/g, respectively. The optimal dosage for synergistic adsorption was determined to be 3 g/L, while pH values ranging from 3 to 9 exhibited negligible effects on the adsorption of both contaminants. The presence of Ca2+ and HCO3− in the solution may interfere with the simultaneous adsorption of PO43−-P and NH4+-N. SEM-EDS and XPS analyses revealed that the primary adsorption mechanisms of PO43−-P and NH4+-N by Mg/Fe-BC involved electrostatic attraction, ion exchange, and hydrogen bonding. In practical applications using chicken manure biogas slurry, Mg/Fe-BC demonstrated synergistic adsorption effects, achieving removal efficiencies of 86.86% for PO43−-P and 36.86% for NH4+-N, thereby confirming its potential application value in wastewater treatment.